I've been trying to develop a provably fair scheme that would work with multiple players (e.g. multiple players each betting on the same coin flip). After doing some research[0][1], I'm drawn to the conclusion that such a scheme is impossible to achieve.
Have you seen Bustabit's solution? They have many users bet on the same bet all the time. Although the site knows the outcome ahead for 10 million rolls, they can't change it anymore to adjust for players' behaviour.
See:
Bustabit (v2) Seeding EventNo, I haven't seen. The ability to immediately verify a bet was fair is part of the appeal for single player provably fair schemes. That said, it's true that by relaxing this requirement (e.g. having to wait a while before verifying a bet), it'd be possible to show that a site wouldn't have been able to adjust for a player's behavior.
I will have a look at Bustabit's solution, thanks for the reference.