1) Unison spread - a way to spread out the panning of the unison voices to create some really fat sounds.
2) Improved FX section - more distortion types, reverb, a way to get distortion on the FX channels as well as the already available insert fx. Other FX always welcome such as compressor
3) A way to control multiple parameters at the same time (mainly for the filter secion). for example I found myself often having to set the filter EG1 mod amount multiple times for each filter. I think I may have read something about an idea holding all 4 filter buttons down to enable control for all 4 filters.
4) Slide/hold notes in the Sequencer - maybe shift + turning the knob enables a slide note?
5) Panning controls at the mixer level for each of the 4 inputs would be amazing. that or either at the oscillator level addition to the already available panning at the VCA level. Not sure if this would be possible but would also help getting some really wide sounds.
6) More Oscillator & Filter types! - Being greedy here as there are already plenty on the Solaris. The models are so good though I would love to hear more. Maybe some more really gritty wavetable type oscillators similar to the ones in NI Massive or I might have remembered seeing there might have been an idea for some kind of user created wavetables. The virus granular & format oscillators are pretty cool.
Thats about it for now - I'm sure I will have more later!