Is this a feasible attack? Is there any other issues?
If the jackpot in your guess game becomes too big, bigger than 25
BTC or maybe even 50
BTC, then yes, this miner attack becomes profitable.
It is cheap to throw away mined block, if the miner itself participate in the game and miner will lose his bet.
For this reason, to give another chance to miner's bet, miner will throw away block that cause game loss.