... what are your views on the prospects or outcomes of a synthesis of atheism (antithesis) and theism (thesis)?
That's a really big question, so I'm going to take the cheapest, shortest route for the moment, until I can manage a bigger answer. The first part is to defer to the second question:
Is atheism "bound" to its reactionary origins?
(1) Yes.
(2) Looking back to notions of synthesis, you're probably using the wrong word; atheism might, by definition, preclude synthesis. Setting aside that bit of pedantry, though, it's all interactive, reactionary, and recursive:
• Data sample: Sometime in the last quarter-century, I think it was, Seventh-Day Adventists encountered a really bizarre problem. There is a practice called "Bible paraphrase", and as dubious as many might find it, we might have expected SDAs to really have a problem, and, actually, they did, but the point was so egregious that they got caught up discussing the particulars instead of the generally bad idea of rewriting the Bible to make it sound better. In this case, and it's been corrected, I think, because the current version doesn't have it, but there was also a discussion guide I don't have access to, at this time, that might be what I saw years ago. I don't mean to be vague, but that's the thing, you're not actually going to believe me: In Genesis 3, when the Lord reflects on Adam and Eve having consumed Knowledge and now need only consume from the Tree of Life in order to "become like us", this portion of Blanco's Clear Word had the Father explaining to the Son that the Fall from Grace was part of the Plan, and people approximately my age might well remember an old atheistic argument about Christendom being a racket that extorting faith in Christ as price to correct the specific Will of God. Christianists loathed this point, and then one of theirs went and handed it out like candy.
• Data sample: There is a possibility that Jesus, as person or character in a story, knows—i.e., recognizes—something contemporary Sufis are known to suggest they've known since before religion proper existed. To the one, it was a Christianist nutjob who handed me that rusty nail. There are many presuppositions that go into it, but that's the thing about literary criticism and the psychoanalytic meaning of history; those presuppositions can be highlighted, and either reinforced or broken. And there is emotional gratification if one can study enough of the history and pay enough attention to what religious people are actually saying; there is, for instance, actually some emotional reward in trading soteriology for a cosmic joke. No, seriously, if we attend Abramism in its own context, high religion was allegedly dead before it ever emerged in Abramic monotheism.
• Data sample: Judaism tracks itself back to the fifth millennium BCE, and by that framework Abraham's covenant with the Lord is said to have occurred between the twenty-second and twentieth centuries BCE. Shamot (Exodus) itself appears to have been codified to its present form in the sixth century BCE. First Isaiah and two minor prophets of the Old Testament, Micha and Hosea, are placed in the seventh Century BCE, with the record of Amos composed or assembled in the late eighth or early seventh. This might seem obscure compared to the generality of the prior samples, but there is still a general punch line. Because the Sufis, for whatever reason, attach themselves to Islam despite claiming to precede all of it, and before there was Islam there was a shahada, and it comes from the eighth century BCE: "There is no God but God, and Salih is His Prophet." And like I said, the punch line is kind of general; it has something to do with the idea that high religion was dead in the Islamic tradition before there was ever a shahada, and coincidentally that latter coincides with the rise of formal monotheism in the Abramic experience among the Hebrews.
Atheism is as atheism does, which is precisely nothing. As a political argument, though, it is indeed bound to its reactionary nature pretty much until it can exterminate all irrationality everywhere in human thought. It's one thing to slay gods; anthropomorphization of everything in Nature to become one simple idea with very human, very relatable tendencies is not going to stop anytime soon. As an evolutionary outcome, we humans have not selected away from these creative and comparative faculties. Nor have we abandoned our curiosity. Questions that defy language often have answers that defy sense.
Some choose vendetta, or if not that some aspect of keeping up with the Joneses, as an atheistic reaction. For the ostensibly rational, keeping up with the Joneses of the lowest common denominators of institutional political religion is something of a roll into the gutter.
Forcing the theistic political discourse to change by leaving it nowhere to go is probably the most obvious manner of transforming the atheistic reaction; by changing the presentation of the theism it addresses, atheistic argument, being bound to react thereunto, will similarly change. Well, you know, unless those advocates don't, and, I don't know, maybe just insist everybody repeat yesterday's caricature, which was also the same as the day before, and the day preceding that.