Twitter, YouTube, Facebook serve a global audience - but the “conservative”/“liberal” dichotomy you describe is unique to the USA.

If social media companies will be bifurcated as you say, it’ll be a tiny fraction of their American audiences - leaving the rest of the world sticking with the mainstream. Those smaller Ameri-centric sites will fail to reach critical-mass needed to sustain themselves in the long-term and hopefully those movements will fade into the background.

Your comparisons to the *chan imageboard splintering is apt, but look at how the more extreme chan sites have been having in finding a web-host (with enough capacity) to host them.