I was really hoping I could build this on top of MTGO or Arena, just as a bot interacting with real Wizards APIs and paying the developers money. But they've got very strong "absolutely no bots" terms of service, and my understanding is that outside of the special case of MTGO trading bots they're strongly enforced with bans. I assume their reasoning is that people do not want to get matched against bot players in tournaments, which is totally fair. (Also I'm not sure MTGO's infrastructure could handle the load of bot users...)