What is your issue with nip07? I much prefer the security/isolation of the interface? I've been (slowly) working on a server-backed extension tool:
https://www.vaughnnugent.com/Resources/Software/Modules/NVault
Discussion
(1) It doesn't work well on mobile
(2) I already have my private key in an app that supports DMs, so if I can log in with that, I'd rather not put my private key in another app
(3) your tool looks very neat, good job!