Multi-site Theme Editor Alternative Flow

Hey guys,
I am making this post to open up ideas on how to allow theme editing in a multi-site environment.

I am moving away from the UserThemes plugin and trying to come up with a better alternative to allow admins to edit themes.

Basically, if a site administrator requests to be able to upload custom themes, the super admin would create an ftp directory, user, and password similar to their WordPress login credentials and give them that information to upload a theme to their home directory (which would be under “/wp-content/themes/blogname”. I would then enable this on a per site basis.

Does anyone have thoughts on this or ways to simplify the flow even further?

(This implementation will be on a limited registration basis and not many users are theme-editing gurus.)