Opt-in replay protection removed from Segwit2x code but it will be probably replaced by something else that will secure both chains.
The reason for removing is; Peter Todd and David Harding found a security vulnerability that would allow LN users to steal funds from each other.
Source;
https://github.com/btc1/bitcoin/commit/98c0af58c29efbecba25818adb5531fa8c3d0506Detailed Explanation;
https://twitter.com/hrdng/status/915967021254414336--
Well basically that means there will be a hard fork with a replay protection or something, for sure. Coinbase, Xapo and all the NYA signers not going to move S2X chain but wait and see if S2X going to survive or not.
If the majority hash power moves to S2X and Legacy Bitcoin blockchain gets weak due low hashrate, NYA companies will have a good reason to convince their users about why they will move to S2X "to protect users money".
That is the first option. Second option is, let's say %50 of the hashrate is moved to S2X. So, Original Bitcoin blocks will be created more slowly, UTXO will grow up and yes network congestion will happen but I think the gap will be replaced quickly.