Excellent points all, glad to see we have some people educated on the topic. Just remember my warnings about US regulation of gambling. The UK's rate of 15% is going to be tough on operators for offering sports, but since most depend on soccer and horse racing for most of their betting activity they can take it for now. Those sports have mostly a tradition of terrible odds for the player compared to North American sports. The low margin of even 11 to 10, let alone -107 or -105 pricing, will be tough to work with at 15% taxes.
As to US states or even federal regulation? That will kill sports betting, the taxes will be at least 20%, maybe more. Casinos online and even poker can handle taxes like that, they are purely system development costs upfront and little else after that other than advertising and maintenance. Other games don't have the cost structure of sports, nor the built in opposition of the sports themselves. I think it will be a long-time in coming to see a workable model of regulation done in the US that will allow a sports business anything like what we see today survive. Ask any operator that posts here if they could make any profit if they had to pay out 25% of just their net win on bets, before they take out their costs. The margins just don't pencil out to handle that sort of burden, but since so many states get away with it as it is I can't see a benevolent decision coming out of this.
I think though the UK, Malta, Latvia, and likely other EU countries will force the hand of the US here. The US can easily ignore Antigua or even a Panama winning a WTO case against them and just pay a fine or whatever, or just try to ignore it. The US hasn't been able to ignore EU judgements against them and any time the matter is between an EU member and a foreign country when it comes to trade, that invokes a coordinated EU response. The US will have to pay attention to that. My guess is the US probably will just begrudingly accept betting happening and maybe a few states set up their own regulated casino-only product. Horse racing will continue to grow. Sports will be left out of it. Hopefully we will be left alone to continue to bet offshore for sports, but it could be a tough road ahead and the fact that US legislators might take a look at regulating this isn't necessarily good for us.