So here is an idea of a provably fair crash system which would work on any standard POW coin's blockchain. It revolves around the target block time, for example bitcoin's 10 minutes. Each 10 minutes that passes without a block being found is multiplier of 2x. If a block was found within 1 minute, it loses everything. This continues on an exponential scale like a normal crash site with a casino edge applied. It works because you can prove that the block was randomly generated by a miner and that a miner wouldn't not publish a block they found.