Brief update to the update:
I've been plugging away at reinforcing the jackpoint and the section of frame rail forward of there into the fender space. Had to remove the fender liner, and was pleasantly surprised it wasn't worse, but it's still not good.
I began welding in the floor pan after tracing the removed rotted section onto a cardboard mockup. I'm overlapping rather than butt-welding, which isn't really the best method, but there's lots of very thin metal that just burns through when I stitch weld, so I need the overlap. Finally getting some good use out of my plasma cutter.
I still don't trust that the chassis has fully regained stiffness, so after reattaching the forward frame rail to the horizontal crossmember, I'm welding everything with the front up on ramps, which is kinda awkward when working in the fender well.
I'm currently wrapping up the internal bracing on the forward frame rail. I'll still add a couple more lateral pieces, before welding in the sheet metal skin. It looks kinda raggedy, 'cause I left little shreds of the good existing pieces of metal intact, though I probably should've just trimmed everything clean. This is not a restoration
. You can just see the piece I welded in alongside the pinchweld running along the bottom of the rocker panel. This is part of the new Jetta scissor jack point. Note that it ties in directly with the heavy vertical piece running up into the pillar