Well it's not that easy.

First the miner needs to actually mine the block.

Second the miner would have replace ETH transactions by his Bitcoinereum ones, that would be transaction that he wouldn't get gas from and so he would get less ETH profit.

That means, if this starts to get profitable enough for miners I don't see any problems if miners start prioritizing their own transactions.

If that happens, the early miners (we) will make enough money already 

So while that doesn't happen we are still in time to make good money out of this