It would be good to clarify that explicitly. Otherwise, if the bankroll is over 10,000 (I know it's not realistic any time soon, but better to have every scenario covered, as there's a lot of money in play here), you could be "taxing" over 100% of profits.
Also, where in the website does it explain the current fee? I couldn't find that.
I've rewritten
https://www.bustabit.com/help/investing to explain the current fee structure in detail and also explicitly state that the dynamic commission rate cannot exceed 100%.
Just for the sake of terminology, lets call the 10k bitcoins, the "bankroll cap". I kind of wonder if having a static value like that is ideal, considering how stupidly volatile btc price is (and that people tend to bet more pegged to fiat value than bitcoin value).
I imagine a "bankroll cap" of something like:
bankrollCap = (15000000000 / $US_DOLLAR_INDEX) / $BITCOIN_PRICE_IN_USD
and refreshing $US_DOLLAR_INDEX and $BITCOIN_PRICE_IN_USD every day or so might make a bit more sense?
I agree that correcting the commission rate for Bitcoin's price would make more sense given that our wager volume tends to be more consistent in purchasing power (e.g. USD, EUR, KRW etc.) than in Bitcoin:
month | wagered_btc | wagered_usd
---------+-----------------+-----------------
2018-01 | 3089.54440200 | $34,121,136.38
2018-02 | 107460.38875000 | $996,376,713.88
2018-03 | 7040.27589300 | $62,256,276.78
2018-04 | 6957.38473000 | $55,414,979.30
2018-05 | 7680.04243400 | $64,872,011.18
2018-06 | 9541.23297200 | $64,930,742.51
2018-07 | 54385.33604000 | $398,807,398.10
2018-08 | 17366.30321900 | $113,090,361.89
2018-09 | 11283.51036500 | $73,694,508.50
2018-10 | 16285.33384700 | $105,458,904.53
2018-11 | 22352.72750300 | $123,457,666.00
2018-12 | 38466.21535800 | $146,456,440.27
2019-01 | 19846.31262100 | $73,070,953.44
2019-02 | 23801.41378000 | $87,914,651.62
2019-03 | 21570.01948300 | $84,647,544.76
2019-04 | 18975.72954800 | $98,037,393.94
2019-05 | 20063.16374100 | $141,976,857.93
2019-06 | 16467.29457300 | $153,353,497.09
2019-07 | 12597.00450100 | $134,437,656.73
2019-08 | 10668.02239900 | $112,786,472.91
2019-09 | 9765.14652500 | $95,310,164.98
2019-10 | 18544.82314300 | $153,762,287.41
2019-11 | 19085.73434500 | $158,654,075.34
2019-12 | 19855.11447000 | $143,982,856.47
2020-01 | 22261.18473100 | $186,435,924.80
2020-02 | 15844.86530900 | $153,348,130.51
2020-03 | 30335.10983900 | $196,404,169.07
2020-04 | 34272.84791000 | $244,552,426.08
2020-05 | 23329.71224900 | $214,882,955.51
2020-06 | 26727.17919200 | $252,317,808.80
2020-07 | 18768.89132900 | $179,021,875.33
2020-08 | 20397.17373400 | $237,097,778.28
2020-09 | 16726.37967800 | $178,179,131.32
2020-10 | 30828.70636200 | $372,183,553.18
However, calculating the commission rate like you suggest is also more difficult for investors to comprehend–especially retroactively–so I'm not sure that's the way to go. The bankroll should find an equilibrium regardless of Bitcoin's price. The only concern is that the equilibrium point becomes too low to support the bets our players want to make or too high for my risk tolerance. While I don't like making changes like this often, the formula is not set in stone and can be changed if necessary.
It's worth considering nevertheless. Maybe other investors can chime in. I'm curious what they think about adjusting the commission rate for Bitcoin's price.