Depends who ‘we’ is. But most people already have a syncretistic religion. They mix physicalism, dualism, ideas with transcendent features with monisms that preclude this, strange contradictory mixtures of ideas of the self - which can be seen in changes during the day in how the self is constituted through language. Most religious people in the west have incorporated ideas from psychology and science and are even influenced by other religions via ideas entering the mainstream from these and filtering back through ‘common sense’ and pop psychology and so on into their habits.
Would you mind adding words to your illustration?
B.t.w.: Happy new year, James!
I was kind of hoping that the pictures would be sufficient.
And Happy New Years to thee as well. 
Basically, the picts are depicting (not through any scientific statistical analysis) that with each new religion, a period of cooperation and social gathering arises but then peaks. As that religion becomes less hope inspiring, a new religion springs up. For a short period there is strong contention between them that fades down but still adds to the next religion. Through time, the total amount of contention keeps growing simply because the degree of entropic particlisation is always increasing (the old doesn’t go away but merely becomes a contentious smaller portion of the whole = entropy).
That situation must continue until someone finally properly/accurately resolves the entire issue of contention. That is what I refer to as the “Right Religion”, “RR”.
But the way of homosapian is that agreement (aka. cooperation) is not sought or revered until substantially yearn for due to excessive contention. Thus the contention must become an extreme (eg. “dooms day”, “apocalypse”) before the answer to proper cooperation and the RR is ever truly sought by enough people to solidify it as a religion.
Once that event occurs, like all before it, the RR contends with all prior religions (including Science) simultaneously, bringing the contention to that extreme. But because it actually does handle contention properly, conversion is inherent, the other religions cannot compete with such extreme contention, the other religions fade away, and the contention then fades out once and for all.
It’s simple.
The pictures are sufficient, yes. But sometimes one has to make sure something.
Let’s have an interim result for the question: „Will we get a syncretistic religion?
We have 67% for „yes“, 22% for „no“, and 11% for „I don’t know“.
Please vote!
I cannot vote as we already have many. This option was not available.
Oh, yes, that option is available. It is the option “no”, because the option “no” also means (for example): “no, we will not get a syncretistic religion because we already have many”. Another point is that the question “will we get” a syncretistic religion?" means: “will we all get one syncretistic religion?”. So I don’t mean merely the Occidental humans but all humans, and I don’t mean a syncretistic religion among other syncretistic religions but only one syncretistic religion, although it is - of course - possible to have also other syncretistic religions included.
So again, Jr Wells: Will we ( as all humans) get one (and only one - thus: regardless, whether there are more syncretistic religions or not) syncretistic religion?
In that case, I voted no.
Brahmanism /Hinduisms, Buddhism, Jainism and others are syncretistic religions or metaphysics (philosophies); and Judaism, Christianity, Islam are - more or less - also syncretiistic religions: Judaism because of the Babylonian / Persian (cp. Parsee, Zoroastrianism), Egyptian, and Ancient Greek (cp. especially Platonism and Stoicism) forms, Christianity because of Judaism (see there), Manichaeism which is also Persian (see there), and Neoplatonism which is also Ancient Greek (sse there), Islam because of Judaism (see there) and Christianity (see there). Beside this famous religions we have also not so famous religions which are also - more or less - syncretistic religions. So you are right when you say that “we already have many” syncretistic religions. But if we consider all aspects, we have to say that they are also not syncretistic religions, because they have developed their own forms too. And in some cases we have to say that all religions are syncretistic religions, because they all trace back to one primeval religion (primitive religion), the first religion.
“Will we get a syncretistic religion?” as the title of this thread postulates “singly” religions, regardless whether they are already syncretistic religions or not; so the question means whether all this “singly” religions will lead to merely one syncretistic religion.
So all we need is one non believer and the answer becomes no.
No. The answer is “no”, if somebody says that we will not get a syncretistic religion. So the “no”-sayer does not have to be a non-believer. Both “yes”-sayers and “no”-sayers have only to have plausible arguments. 
I mean, in say 1 million years time, when we have one religion left and all 3 Bazingallion humans on Earth and Mars believe in it… Except one (he believes in something else). Then we don’t have a syncretistic religion.
I know what you mean. But what does that have to do with the question as title of this thread? It postulates „singly“ religions, regardless whether they are already syncretistic religions or not! If someone believes in something else, then that does not necessarily mean that this one can prevent that the other believers will not get a syncretistic religion. This single, and probably lonely, one believer does not represent a religious community. You know what I mean?
Okay, instead of “we all” I should have said “most of us”. But therefore I have a counterquestion: Would you avoid the words “manhood”, “mankind”, “humankind”, “humanity” just because of the fact that there are some people who do not believe in “manhood”, “mankind”, “humankind”, “humanity”?
Q: Is there allowed to be non-believers in a syncretistic religion?
A: Yes, but “most” need to be believers in that religion for it to be syncretistic.
Q: Can we have more than one syncretistic religion?
A: No it must be one and only one
There will always be people who deviate from the norm.
This deviation will not allow “perfect” syncretistic religions to form as these people will be excluded.
Q: Was it allowed to be a Non-Roman in the Roman Empire?
A: Yes, but most needed to be Romans in that emprie for it to be a Roman empire.
Q: Could the Romans have more than one Roman Empire?
A: No, ist had to be one and only one.
There will always be people who deviate from the norm.
This deviation will not eternally allow one perfect and eternal Romam Empire (therefore Jesus said: “My empire is not of this world”), but temporarily it is possible.
Temporarily one syncretistic religion can exist, if deviation is allowed. Later this syncretistic religion will decay. Everything deacys, but temporarily it can exist.
That is why there has never been a single empire in the history of human kind (prior to nations/empires there were clans).
People will always differentiate and break away and start there own thing.
Edit: The system will not allow for a temporary creation of a unified whole. I am trying to think of an analogy but my brain is a bit fatigued at the moment (I have a lot on my plate).
What “system” is that?
We can think of many analogies in that case. For example: Each living being has a so-called “individual” body, a unit, although there are many other living beings in that body, if this living being is a so-called “higher living being” like a human being. The other living beings in that one living being are the deviations of the rule that one living being is always one living being. It’s right: one living being is one living being, regardless whether there are many other living beings in that one living being or not. Beyond that: this one living being needs the other living beings. Living beings are beings of self-preservation (including: self-organisation and reproduction) with an immune system; and the immune system of a so-called “higher living being” depends on other living beings (bacteria / germs).
Without deviations a syncretistic religion can not exist, but we have to call it “syncretistic religion” nonetheless, even then, if some people who are part of this syncretistic religion say “we do not want to be part of this syncretistic religion”. As long as this deviated people of one syncretistic religion are not too many, the “immune system” of that syncretistic religion works very well, thus that syncretistic religion is very “healthy”, exists very well.
If there was a “pure” syncretistic religion already in place and it had a specific doctrine in place that maintained itself… then I would agree with you but to get to that point in the first place is, I believe, not possible. The same question could apply to politics; and I do not think that is possible either.