Here's my thoughts on playability:
Yellow, Red, Orange, and Hot Pink (the one in the bottom right corner?) are all fine for now.
Move the border between Orne and Manche up just a tad on the left side, to make it clear that Manche does NOT border Rennes (I'm assuming it already doesn't, so that's just clarity not any change in the borders).
Put an impassible border across the entire north side of Paris, cutting it off from Eure, Oise, and Aisne. This also reduces the total borders for the pink region to 3.
Put an impassible border all the way around Indre and Cher (Indre should only border Loiret and Cher now, Cher no longer borders Creuse). This reduces the total borders for the blue region to 4. Both of these together should reduce green to 4 borders.
Extend the mountains between Drome and Gard so that Lozere no longer borders either.
Add an impassible border along the south edge of Dordogne and Lot (Lot now only borders purple territories, Dordogne still borders Charente but not Aquitaine). These two together should reduce purple borders to 5.
This should make all the outside regions holdable, the two in the middle very hard to hold but not impossible if you or a teammate hold a neighboring region.
We'll see how it looks after that and talk bonuses.