This is encouraging. While you are considering how this might best be done there’s something you should take a look at.
I have an app version of dweb ready for release. This uses the new dweb-server library to integrate the REST endpoint into the app so it’s like dweb serve with a GUI. No more command line 
Adding the wallet here will be a bit like adding it to Friends, giving users a nice GUI and a server that is always running (by me adding auto start functionality). It will also ensure that private keys are only known to this app. And it will work with Friends, Atlas and any other dweb apps.
So it’s a great place to integrate a wallet. You have direct Rust access for short term (eg using an ACT lib) and can add routes to REST later if that makes sense for dweb apps, though they might not need much. I think this fits with your plan as described above.
For the moment the dweb-app GUI shows any wallet picked up from the system (feature added by @riddim 
) but could include a way to create or select different wallets.
Take a look in the dweb repo. You can run it there with cargo tauri dev.
I want to add auto start before release, so maybe next week.