Wow, lots of things ^^.
1) This may be reconsidered now there is the overdub feature. You exactly get why I thought it was not that important before.
2) Well, I could add a tap-tempo button to the metronome generator. But the pre-recording metronome is unlikely to happen, the combination of a click-track and quantized recording does this trick for now. Even if it may not be handy if your loop is like 32 beats at 80 BPM :p.
3) Time stretching is cool, I agree

. I would like to do it, not sure when, it's a quite time-consuming task.
4) For that I think upgrading all tracks to stereo and being able to balance L and R channel would be nice. I'm working on it right now.
5) That's something that is high on my priority list.
6) That's not planned, I still rely on your fingers for doing it ^^.
Thanks for taking the time to write me your wish-list, that helps me to prioritize features over each others.
Cheers,
Raphaël