If I understand correctly you are hoping to setup an exit node where the outbound user traffic that would normally go to the clearnet winds up going through a VPN first instead?

I'm not sure this is a very friendly idea for the Tor network. At the very least, it's introducing an extra hop and additional latency. The average Tor user has no ability to easily detect or opt-out of this situation. At the worst, depending on how the VPN is implemented, you might introduce other performance issues (TCP over TCP tunnels comes to mind) or security issues (DNS leaks, VPN provider now has the ability to sniff traffic, etc.).