I'm just reasoning on an already existent NIP that has low support, trying to improve it, and yes I'm interested more in key rotation, because I think it's more urgent.

I agree that to solve this specific problem would be better a dedicated solution, and probably there are many. For example I thought about hierarchical deterministic wallets, exposing the master public key and use an event to signal the height of the valid key.

Btw, delegation with expiry is actually key rotation. They are two problems with clear common points.
But a clear limit of NIP-26 in this respect is that it not allow for immediate revocation.