Well, a lot of the important stuff has been mentioned already, but I'll add a couple of things.
- Effect plugins applicable to a single channel, an x number of channels, or the entire mix. Preferably with an open API, so that 3rd parties can also write new plugins.
- Disk writer supporting at least WAVE and AIFF, maybe even OGG (MP3 would probably bring licensing problems?). An extremely cool feature would be 24bit/96KHz quality support here.
