The debug system certainly needs to work better. It crashes more often than I actually use it 
(no offense to you guys writing and supporting the PDE. I’ll provide examples on demand if needed)
Aside of that, I’d expect just one feature of the Processing IDE: support of the adjustable TAB character in sketches… I miss it so much!
But in general I think the PDE should be as it is: simple, welcoming to beginners, easy to get started yet powerful as long as you dig in.