Then what do you do if there is a huge swing in the value of btc? You have to start taking this into account too... maybe in two years betting 10 btc is like betting 50 now? I foresee endless discussion about the level at which the house edge should start going up. Spare us the aggravation and just leave it at 1% for all bets.
I assume it would be written as a percentage of the bankroll. For example:
"you can bet to win up to 1% of the bankroll with a 1% edge and up to N% of the bankroll with an N% edge" (for some N)
Then it automatically scales with BTC price, as the bankroll adjusts.