Subclassing an app?

I’m trying to make a publish tool for use in SG desktop; it’ll have a fancy UI but otherwise be pretty similar to tk-multi-publish2. I’d like to avoid duplicating and modifying tk-multi-publish2 – instead I’d like to inherit from it, creating a subclass. Then just override the parts of the UI that we need for our workflow, leaving the rest to the shipped tk-multi-publish2 code. That way it should be simpler to write and more maintainable.
Can this be done? I know that an app is an instance of a subclass of sgtk.platform.Application, so can I make a subclass of another existing app? I’d love to see an example of this.

Anyone have any ideas on this? What do folks here do to make an app that’s similar to an existing app? Just fork the original?
I made some progress on subclassing an app, but eventually hit a wall – tk just does too much module loading trickery.

Forking I’m afraid!