They'd be switching over to an alternative chain though. That chain, at the lower difficulty, would not overtake the existing Bitcoin chain, as it is the total weight of proof of work, not simple number of blocks, which would determine the chain used by all legacy nodes (including, you know, the ones that are used by the exchanges). We'd literally be looking at another BCash scenario. It is true that if a large portion of the hashrate did move over to the split chain, it would then ramp up in difficulty (as the legacy chain dropped) and thus make a huge reorg possible as if it did finally overtake the legacy chain, those legacy nodes (the vast majority of Bitcoin nodes) would suddenly reorg their chain to the 110 chain. At the minimum 2 weeks worth of blocks, (plus whatever time it takes to overtake it with more proof of work). I would think everyone would recognize this as perhaps the worst possible outcome (unless you're that hellbent on getting sats cheaper -- because you very much will).