The hard part is the banking and payments side of things. That's where a new entrant would be useful (but unfortunately also ~impossible in the US).
If you can find a gateway and processor that has an underwriting team that will not require an FFL, that would be a sight to behold.
I am not sure why the banks are so puritanical.
[0] https://www.paypal.com/us/smarthelp/article/what-is-paypal%E...