Philip two things. First, and for Ethin as well, a VST can have more than just two channels as input, especially in DAWs like reaper, and if you're gonna make it VST3 assume something powerful like that, you can have 1/2 and 3/4, 1/2 bing the modulator and 3/4 being the carrier or whatever. You might even make two separate versions, you would need different dll's because this is probably done on init, or you could check filename, but you could have a mono input version with 1/2 being mod and carrier, or 1/2-3/4 with the stereo pairs. I'd love to see how this thing deals with input where I use a stereo carrier and stereo modulator but the stereo modulator is off center and the stereo carrier is in the other direction. Still this already a big improvement, just about no vocoders, even some hardware, support stereo for both inputs and give a stereo output.
And the second thing: Can't you use GitHub's release system for this so you don't keep having to create new dropbox links? I've seen a good few release binaries through the release system as assets.