if they made JP8s a lot of 7 string and 8 string players would buy them, simply because of the reputation that the JP7 has. but you're right, that number would still be small, relative to EBs other models
Honestly I think an 8 would sell better than the baritone 6. However John uses the bari. So as said it will probably only happen if John wants to venture into 8's.