As I said before, if miners wanted to stay on the old chain,
IMHO it's not a problem of miners. No miner would stay on a chain where minted tokens have no value at all.
I think the real question is whether or not there's the need of a coercive tool to "force" the migration.
@ppratscher "I suggest to replace the current block logic with a simple
if blockNbr > BOMB_NUMBER then block.difficulty = uint64.maxvalue this way we keep to bomb alive but avoid the unpredictable block times"
That is an eminently sensible suggestion, IMHO, but maybe with the block number a LONG WAY AWAY, like 2 years.
And then reduce the block number at the time of the last HF prior to transition.