I think in your current UI setup you request the user input the npub, and that in the backend is used to specify the filter "#p":["hex pubkey"] ...?

I think that works great.

I would only need another field, similar to the current "Write" node layout, where you request the user input the Kind, with default to 1.

I use that a lot to write other kinds like 7 (reactions), 5910 (DVM request), 9734 (zap request), etc.