I'm loving the crisp, tight sound of the Virus - it's making me realise what I've been missing with a lot of soft synths. However, there seems to be a growing fashion for additive synthesis - and the sounds available using an additive synthesis engine are interesting, diverse and powerful. Software synths like Razor and Harmor have shown that the seemingly bewildering concept can be broken down into an easy-to-use, familiar format.
It would be really interesting to have the ability to swap out a couple of oscillators for additive oscillators (with a selection of pre-created additive waveforms) and plug in a pair of additive processors while still within the additive engine, before it drops back to the subtractive engine to use the classic filter and effects sections. I think this 'best of both worlds' approach would give the Virus a unique edge.
I do, however, accept that the amount of development time and processing power required may well be prohibitive.