No one has any hard proof i've seen, only speculation. given ABC's devs public attacks on SV devs, but when asked silence some infer they may work for Bitmain. who knows.
Bitmain is not the entity I'd like in charge of BCH development. Too much stake in the shitcoin racket. I think they won't make a BCH that could take all their non-SHA256 business away
The non-sha256 business is minimal, I doubt it exceeds 20%, more like around 5%. I don’t think ABC is the right way to go anyway. I am all in for Bitcoin Unlimited.