Windows 10 can already do this by default.
> remove registry entries for software that's no longer installed.
Uninstalling old style Windows software is a hard problem that generally can't be done in a foolproof way, without potentially breaking stuff, due to bad legacy design decisions like giving programs free reign to install stuff wherever they want, without a proper application model nor dependency tracking. Therefore, registry cleaners are also prone to break things.
https://support.microsoft.com/en-us/help/2563254/microsoft-s...
> That sort of maintenance seems like it's the result of poor design in an OS that has the hood welded shut.
That's what UWP solves.
https://np.reddit.com/r/Surface/comments/6ifyxq/spotify_for_...
> It also let me simply check and disable startup programs
This is already in the Windows 10 UI.