Thats a gamble on the miners behalf. BCash implemented replay protection, which resulted in two coins that people freely traded. I think the lack of replay protection is what will be a driving force within the user community. The miners will make their choice on the prediction of what the users will do. It should be easy enough for a miner to switch from one to another, but still sometime is needed to shut down, swap the code and bring it back online.

Not being a miner, or a large user of BTC (other than speculating money on it), its difficult to say which way we are heading, because the reality is that the user community (traders and alike) could go any which way...even by accident.