It would be better if you could find a way of making the jackpot provably fair.
Under the current rules it would be trivial for you to delay a bet by a fraction of a second to ensure its betid is non-prime if the "wrong" player is about to win it.
Why have this prime number requirement at all?
edit:
Do you realise that this means the house edge is smaller for tiny bets than for big bets? It will encourage smart players to make smaller bets.
Finally, since the Unix time is prime about 1/22 of the time, and the betid is prime about 1/20 of the time, and you hit the required number 1/10000 of the time, betting 1 satoshi will hit the jackpot about 1 in 22*20*10000 bets. That's 1 in 4.4 million bets. But the jackpot is 20% of 1 BTC, or 20 million satoshis. That makes the jackpot very +EV:
>>> 100 * (1 - 20/4.4)
-354.5454545454545
The house edge when betting 1 satoshi is minus 354.5%...
Actually we have a verifier system on the stats site for that I believe. As well as full announcements (automated in chatr so anyone can check their rolls at any time if they felt they had it mate