Regulatory requirements are the hard part. The governments (of many different countries) are by no means required to license you to do what they do - it's not just a storefront, it's tons of financial regulation, they're even fdic insured for cash deposits. It’s a legal challenge
but not much beyond that. almost guaranteed profit
Not sure that's true. Absolutely massive target for blackhats. Security has to be off the rails good
No bank would service your account. At this point you need to found your own banking charter like ItBit or Gemini.
FairX is an near-term project assumed to be targeting this space.