Ardour Plugin Pack
While VST and AU support are being worked on, I think something cool would be if Ardour came bundled with a plugin pack of some essential software synths that make use of LADSPA, DSSI, JACK, etc.
It would be a good way to encourage development of native soft synths for linux. I can imagine there might be some place within Ardour where you can access the built-in(well not really built-in, but more like bundled) synths. I'm not talking about a huge number of synths. Maybe RTSynth, amsynth, and a couple others.
I'm sure there's tons of software synths that don't get any attention, but would be put to great use if there were only a few mouse clicks(or keystroke) away in Ardour.