Ya know, in a way, this actually temporarily decreases the difficulty to generate blocks until everyone upgrades. Yeah, it’ll be slower, but that just gives each client more time to try to generate the difficult hash.
Of course, this happened right after the difficulty kicked up to 511.7, so all these new “good” blocks will have to contend with that. And a good chunk of the network grind power is off on the wrong chain, so new blocks may take a lot longer than 10min to find. At what point will the balancing figure this out and possibly kick the difficulty back down again?