Yeah, difficulty adjustment I can do. I would just start at some difficulty, and announce ahead of time (maybe 6 months ahead) of the new difficulty. People would have to roll over their device keys before then if their PoW wasn't already high enough.
But I think ynniv (npub12ak…6fdh) 's point is the biggest problem. People's hardware is just too variant. Smartphones can't compete with spammer dedicated hardware, so there is no PoW which is easy enough for a smartphone and still too hard for a spammer with dedicated hardware.
And my point about the key generation not being the gating factor also has convinced me that this line of thinking is a dead end.
