Control Surface Matrix?
I think it would be a good idea to start a wiki or something with all the control surfaces supported by Ardour similar to the ALSA Soundcard Matrix. It would make it much easier to check compatibility, especially with control surfaces coming out now that use ethernet or a proprietary protocol instead of MIDI, etc. (Eg: Euphonix MC Control/Mix or the Frontier Design Alphatrack)
Another point is wouldn't it be a good idea to create a API library to let other Open Source applications use control surfaces that have been implemented such as the Mackie Control Universal instead of having to rewrite code? I'm not sure if this is done already but I think it would be a very good idea.