I'm about half way saved up for this system: 
The idea is to have a self-contained performance system that can range from booty shaking music to rhythmic noice. I figure between the Metropolis, Trigger Riot, and the uStep, I'm good for sequencing and modulation sources, not counting the LFOs from the Atlantis and the Tidal Wave.
I plan on doing this in two waves. The upper 3u (main synth voice and sequencer plus effects) will be first. Then the bottom 3u (drum sequencer + voices, Tidal Wave - mostly for envelope/filter/etc, but also as a secondary voice, and a mixer) will come toward the end of the year.
It's all pretty straight forward, but I can't help shake the feeling I'm missing something.
Thanks for any input.