If you deposit, lose, and then double spend your deposit, then the casino/sportsbook in question has only lost potential profits (your deposit), and hasn't actually lost anything from their reserves.
Sure, but the point is you gambled for free and didn't lose any money, while leaving the option to make money open just in case you won. The casino also didn't make any money on your losses, which they should have.
I wonder how many such places will continue to offer zero confirmation deposits after full RBF becomes widespread. Very few, I suspect, since it them become trivial for anyone to double spend a losing deposit.
Crypto casinos haven't been the fastest ones in the past to introduce new things, like SegWit for example. I remember it took some popular platforms years before they updated their systems to allow withdrawals to Bech32 addresses.
This time around, it's their profits and their money that's on the line, so they might be somewhat quicker. I still think they will wait to see what happens. And if they realize there are many players that abuse the zero-deposit feature, they will just disable it for new accounts while probably not doing it for longtime and loyal players.