A custom virtual machine and wifi. As a user, I'd much more appreciate exercises of modularity than featurefullness. Not that I don't sympathize with the maker. Over-engineering can be fun.
Modularity was actually a design consideration I really struggled with, but at the end of the day, I realized I didn't want to do just another Arduino clone where you put the whole thing together yourself. I designed Chromatron under the assumption that you'd eventually end up with a lot of them, in which case the Wifi and live coding are really useful features - I wanted and all-in-one solution. But for most people who only need 1 or 2 projects, it's overkill. I think that's part of the reason it didn't sell that well.