The NY agreement stipulates that the two are tied together; that by signalling bit 4 they are voting to activate segwit AND the hard fork down the track. They did this in the hope they could get their (useless) block size increase after activating segwit. However there is absolutely nothing that guarantees the lock in of the hard fork 3 months from now based on bit 4 being active at the moment. There is nothing stopping all the miners from simply dropping the btc1 fork code and just using core after segwit is activated, and not all pools actually signed the agreement. Heck there's little sign anyone's actually using the btc1 fork at the moment. Likely they're all custom patched with segsignal just for BIP91 as my pool is.