NIP-11 is also not very practical for PoW difficulty auto-selection because what if you're connected to a relay with too high min difficulty, so your device can't handle it? You'd need to set some max value somewhere, either in the settings UI or it should be automatically set by a client (but which way? by running a benchmark?). Having a PoW difficulty input field somewhere is almost inevitable. It'd be great to set it only once.