Update, I tried playing a custom game, 1v1 against AI, and it loaded, everything worked, but the lag was horrendous even on the absolute lowest settings.
This does at least confirm for certain that, at least on my end, it's an issue with how the game's interacting with my Nvidia driver. Question now is why, and why it was working a few days ago, and what Taleworlds can do to fix it.