I know this may be a huge PITA beside not being very useful to the majority of users, but there are a few people working to implement "multitouch" interfaces to Linux. MPX is one that is coming along nicely by adding the ability to have multiple mice or a multitouch screen for the X server. However, the app has to take advantage of this.
My first thought is the ability to control the mixer on either a multitouch screen or with two mice, but Ardour has to respond to the second mouse or second touch point.
I may not be a necessary addition, but a youtube video of someone controling ardour's mixer almost like a real mixer would be great publicity.