I’m super interested in Midi Guitar, but I don’t want to spend money on something that is no longer receiving support and updates (we’ve all been there…)
Is JamOrigin still an active company? Is there still active development on Midi Guitar 3? And active patching / updates on Midi Guitar 2?
Yes!
MIDI Guitar is still active. MIDI Guitar 3 is very much in the making, but you should not expect any patching or updates to MIDI Guitar 2 until version 3 is out, unless something breaks of course. Hopefully, you guys shouldn’t have to way too long now, but I can’t give you a date for the release yet. I hope you understand.
Hello Dave, welcome to this forum 
If you take a look at this forum’s sections, you will see that it is always active, and that people who ask questions generally receive answers fairly quickly: the proof in your case. 
The current version of MG already more than justifies its purchase, and as @LoFiLeiF said, the next update has been under construction for some time now, but this wait is justified mainly by the complexity of audio-to-Midi conversion and by the importance of the features to come.
MG is a really powerful and efficient tool that I have been using every day for several years now, and I could not do without it, mainly for live performance but also for the simple pleasure of practicing Midi instruments with my guitars.