I'd love to see some Korg synths. I know the MicroKorg is still alive and kicking, but I'd still love to have a good software emulation of that. If nothing else, it had the same engine as the MS2000, and technically the MS2000 is historical relic at this point (hint, hint). Also,
Korg MS-20
Korg Wavestation
Alesis Micron/Akai Miniak
And I have to say it, just imagine what Arturia could do with the Casio SK-5 Sampler!
Oh, and how about some kind of supercharged Theremin (ala the Theremini), packaged with a hardware controller (or integrated into Keylab MkIII)