Dynamic effects would be good - a compressor (single and multiband), a mastering limiter, gates, etc.
A analogue-type tape-echo would be nice (I know you can do this to an extent with the delay "colour", but you can't attenuate the highs and the lows to leave the mids at any one time, etc.)
More distortions would be kewl. Maybe even a saturation effect that sounds like proper saturation, tape/valves/opto etc., without it sounding fizzy and sapping all the life away from your patch. The PSP Vintage Warmer sounds great, for eg.
I always liked Step-Sequencers too. I know the TI will employ a customisable arpeggiator, but I think is limited to just modulating velocities and note-on/off data? Modulating any number of parameters (and not just note-on/off data) would be seriously cool. You'd be able to do some serious filter gating, etc.
And, er, maybe I haven't mentioned it yet, but importing of user wavetables in the style of Z3ta+ would be jolly nice!!
