In my experience remote signing with nostr keys works well enough and doesn't seem to be the bottle neck since a signature is only needed when the user is taking an action so any delay can be handled with a loading screen. Remote decryption is more of the issue since its slower than signing and usually requires more than a single call (user opens DM conversation). NIP-59 just makes this worse though by 2x the number of calls I don't know what a good solution is but I don't think its key delegation or derivation since that requires either a messy permission language (NIP-26) or a extra metadata layer or changes to the relays 😞