For me, just having a simple, reliable bag drop would be a big win.
This time around, Loudeac would still have suited (I got there at 2pm and again at about 5pm the next day, so it wasn't an overnight stop). Just to get a change of clothes, battery swap, refill on food - making three 400km legs.
Personally though, I'd love a double bag drop even more - Fougeres and Carhaix perhaps (off the top of my head). Then I could reprovision at (roughly) 300, 200,200,200,300 intervals, which would be neat.
I've "done" PBP as a touriste. If I go back, it would be to go a bit quicker, which makes provisions pretty useful. Would definitely pay for something along those lines.
I'm not sure having a physical helper would be at all straightforward, given how wildly different times people will be at different controls (between 90 and 84 hour start, to being with!)