The tubbutec MIDI retrofit looks like a great product with outstanding functionality (I *love* that he offers graphic overlays, too). But, it's not open source. You can't modify the software. Therefore, it's not extendable. If I am inspired by some crazy idea, I cannot easily build upon it's great features to make something new.
For a lot of folks who want plug-and-play, this looks like a fantastic solution. But for the hacker/DIY crowd, there's still an opening for an open-source project.
Chip