It also changes the installation and configuration process considerably, making this a more traditional Python package.
However, applications are meant to be portable to this system with very little effort. You may encounter a few NotImplementedExceptions for some methods that seemed obscure, but API compatibility is a goal, and any problems can be submitted as a bug.
Paste WebKit reimplements a stable API. Paste WebKit itself is very stable. This is primarily a bridge project for bringing old Webware code into the WSGI environment. No non-bugfix development on Paste WebKit is planned.