Compressor & Limiter
Filter Q Normalise (like Novation KS-Rack - to compensate for level boost with high reso settings)
Side Band & Comb filters while were at it
Uploadable wavetables
Cross patch FM operators for Multi mode
Morph groups (single mode), or cross patch morph for multi mode (not via fade - but via actual patch param morphs)
Actually - to hell with it - while not go the whole way and add an extended multi-mode thats a 'monster modular mode' - combine a bunch of patches with cross patch mod destinations etc, stacking loads of filters, layering loads of oscilators, hijacking loads of lfo, eg and others mod sources and assigning them to whatever - probably need a G2 modular style drag and drop editor for it
OK - so thats all the silly stuff
On a more realistic note:
A bunch of options to control the extent of 'Integration' to assist us folks who want better hardware studio integration without having to abandon virus control, even if that only leaves VC as a patch editor, multi-editor, seq-mode editor, librarian, arp editor etc. (ie switch off all audio and ASIO based audio, and switch off using midi ports as computer midi ports, leaving them as virus private ports, as per novation X-Station/Remote boards)
Standalone version of virus control (ie as a .exe or mac equiv) that also will serve as Multi mode editor and Remote editor (when remote gets done). Maybe the standalone version should be yamaha studio connections compatible as well - though I think the Yamaha UIs are ugly as hell, but the concept good.
Remote mode that aint just aimed at remote control of software, but also leaves the MIDI port active (under virus control) so I can fully control my ES Rack as well from the TI keyboard (even while VC is running) - ie as implemented on Novation X-Station/Remote boards.
Semi-tone key transpose via SHIFT+Transpose buttons (keyboard/polar versions only probably, or maybe all according to key/engine setting) - should also work in remote mode as well.
Split Synth + Remote mode - for eg - assign top 2 octaves and all controls except soft knobs, pedals, and pitch/mod to remote, leaving everything else driving the virus engine.
OK - thats probably enough to keep the dev guys busy for a while