Some ideas, which I hope might help;
First, my experience with the quick panel has been with file lists and command lists. As yet, I've not needed to do multiple selection of the list; can you explain what your scenario is? The quick panel doesn't do multiple selection, so I can't quite see what your situation is.
I'm not entirely convinced yet of the need for regex. My experience is that the behaviour of caps is great -- It's better than regex for filtering a great deal of the time. Certainly, if I know that I'm looking for a file called 'AbstractExampleReader.cs' then I'd much prefer to type "ABEXRE" than "Ab.*Ex.*Re.*". The regex is much harder to compose.
Case is also an issue. lcase currently means one kind of matching, and ucase another. What do you do with mixed-case regex? How do you indicate the start of a regex? Whether it's case-sensitive? Sublime uses a toggle button to turn regex on and off, so that'd need to appear somewhere in the quickpanel, making it a little less 'quick' and more a full tool window.
I like the idea of a 'not' operator, though. I haven't needed it yet, though.
Anyway, not a coherent post, I know -- just trying to explore some of the issues.