All right! It's about time someone starting rethinking the idea of a tracker (probably the only was I'll ever make music on a computer).
My biggest complaint about ProTracker was the awful GUI. But then, I never liked the "standardized" GUI used in OctaMed 5, and later, OctaMed SoundStudio. I think the MED 3.0 interface is pretty much ideal. :-) But hey, this is ProTracker, not MED. Any ProTracker upgrade will be appreciated!
Features and gizmos are nice, of course, but the only things I'd really like to see different about any tracker includes sample compression and stereo/sensurround support.
Compression is really mandatory. Sample quality has improved a lot, and with stereo support, mods can get really huge. It really annoys me when 3-4 meg "modules" start showing up, in which case you might as well just make an MP3. Besides, decompression is REALLY getting insanely fast these days. I'd be more opt to support OGG compression. It's good, free, and free of patent issues (for now), so people might as well.
I'd also like to see proper panning and sensurround support. Panning was possible with FastTracker, but a real pain. I'd be nice to see what people can do with sensurround audio, too.
Personally, I think filtering, echo, reverb, and other audio effects can wait. I would just like to see a new interface, for now.