I got a great reply from a redditor in the r/startup_ideas subreddit.
You still cannot offer wagering unless you obtain a gaming license. Providing a peer to peer service that you charge money to facilitate is the same as offering gaming. Your only hope would be to take no money. But even then, see below.
Once states pass specific laws permitting sports wagering, big mind-space companies like Caesars, MGM, etc will enter that space with millions of dollars in marketing muscle.
If current poker and casino legalization is any indication of what will happen with sports wagering, even applying for a license will cost millions. Pennsylvania is charging $4 million each for online slots, online table game (i.e. black jack), and online poker licenses (i.e. $12 million total, but PA has been kind enough to offer a discount to $10 million if you take all three).
Nobody that pays these licensing fees or has to operate under stiff gaming regulatory oversight is going to take kindly to your product in their market and will lobby at the highest levels for state or DOJ enforcement.
Similar to the above, gaming typically has a special tax rate applied to wagers. A casino pays tax on GROSS revenue. Some states are talking about taxing on handle (amount wagered) for sports betting. The amount you owe in taxes could be more than you collected in fees.
NBA, MLB, and NFL are trying to muscle in and force potential sports betting platforms to pay an integrity fee (to make sure the games are fair - really just a cash grab). Presumably, your app would also have to pay an integrity fee to the major sports leagues.
Virtual currency does not solve the problem. If the virtual currency can be exchanged for anything of value then it is wagering.