So finally B2X is happened today on block 494784 despite the lack of consensus in the last week. Coinbase has already disabled the transactions of btc.
Last I heard, btc1 nodes are stuck as of block height 494,782.
According to Core developer Alex Morcos, everyone saying that the forking height was 494,784 was incorrect. Apparently, the last common block is 494,782 and 494,783 is supposed to be the first forked block. That assumes that miners actually mine a block. Given that the difficulty was not adjusted downward, this seems unlikely.
What will be the effect of this fork on BTC?
Unless miners become irrational and start mining 2x, it should be a non-event. The difficulty is quite high, so mining it is probably just burning money. I'm really surprised that Coinbase bothered with this after all the other companies (including Bitmain) backed out.