if your team has a fox RSN, you can already you can already stream in market without a cable subscription through sling
That's a good point. I've never read a reason to why they are allowed to do that. MLB could treat those services the same as they do Sat/Cable and not count that as streaming, or selling to them is part of the waiver they've leased back to the rights holders. Since it seems to be all the same teams on those services as the ones that also offer in-market streaming, I suspect it is the latter. In that's the case, and there is no renewal of agreements, then games on those services will be blacked out.