I have a feeling this is beyond the scope of the project for various reasons, but it couldn’t hurt to ask. I use pinentry for GnuPG password entry (via enigmail in thunderbird primarily, but also for file operations in both windows and linux) multiple times a day, every day. I use autotype in keepass right now, and manually select my key from the list every time (the window title does not change based on PGP key). It seems pinentry supports allowing an external password manager to store and provide the password (something to do with an external cache), which at least gnome-keyring offers on linux systems with it installed. It would be nice to be able to get the password from keepass the same way other dialogs subject to Kee/KeeFox do.
Having stated the request, I expect this would either require a new (likely daemon-style) plugin to be developed or that functionality added to KeepassRPC, which seems to extend beyond its intended form. Both seem a bit unreasonable to ask of this project. If I’m wrong and this is a reasonable request, I’d love to see it happen.