A bit of progress on the Très Riches Heures gown: I've done the preliminary fitting, so it's not quite so oversized. I cut back the lining to match the adjustments to the fashion fabric, and started assembling that. I went back and cut the gores for the lining as well, since I had neglected to do that originally. It may still need to be taken in further, but its starting to shape up. Once I finish assembling the lining, I should be able to set in the neckline and armholes.
As it currently stands, the gown is cut a bit beyond floor length, the idea being that it would puddle on the ground, but the fabric just has too much body to 'puddle' properly. I'm debating trimming the hem down to just barely floor length in the hopes that it might drape better (and be more likely to be worn, honestly), but it might actually make things worse instead. Looks like I'll be perching on stacks of books in the near future to get an idea of how it would behave.
This is probably a bad sign, but I've starting thinking about contingency plans for what I could re-cut the fabric into if this gown doesn't work. A late 16th century forepart skirt is near the top of that list.