I just gave Microphone Mode a quick try using a Rock Band microphone that's already connected. The output simply wasn't hot enough to work reliably, which the calibration warned me about. I suspect the mic doesn't have the most amazing frequency response curve, but I'll try it on a microphone stand before trying to set up a more respectable microphone with a USB interface. It was, however,, enough to make me think it could be a tool to incentivize practice. Even Disconnected Mode looks useful in that regard.
On a less positive note, the damn crackling input issues really are still present with this patch. Not only that, but they affect Microphone Mode as well. Bleah. Do they have no idea what the issue is, or are they just willfully ignorant of the fact that it exists? Either way, it's incredibly irritating.