Can't go wrong with the MSSIAH cart, that thing is amazing.
I was just about to pull the trigger and get a C64 reloaded board to build into a MSSIAH based system, but then once I got things converted to US dollars and realized how much it was going to cost to get the board, MSSIAH, etc I got cold feet. It was going beyond $400usd which is breaking my budget. Maybe if I lucked out on a free or near free C64 to use for it I would think differently, but even for-parts C64s are selling for a minimum of $50 with shipping. LSS, I'll certainly be keeping an eye on this thread.
That's just about it. Should I have a functioning VST already this would be a whole different scenario.
I've gone too far and really want to push this thing through so I've decided to make the proto-run with my own money. That will eventually settle the question whether the VST is possible. There's also the possibility that this yet untested design is faulty and can be just a waste of both time and money but as long this doesn't bankrupt me I think I'm fine... a guy's gotta have a hobby, right?
Should the design work as expected I could maybe sell these prototypes exclusively via chipmusic.org and should the VST become reality, I can easily make a larger production run... wish me luck.
Cheers,
emBLIP
I'm totally naive to this stuff, but had you considered basing it off Midibox SID? I think Midibox has a USB/Midi module.