"Bitmain ETH ASIC" is not an ASIC, look here for some hard data:
https://blog.bitmex.com/nextstageinmining/
And POS is a highly dubious, potentially dangerous and hard to implement IDEA
https://blog.bitmex.com/complete-guide-to-proof-of-stake-ethereums-latest-proposal-vitalik-buterin-interview/
Also, a move to POS would make ETH tokens fall into "securities" category.
https://news.bitcoin.com/ether-ripple-doomed-as-securities-according-to-regulation-expert/
I think ETH POS will not become a reality any time soon.