I don't see any. I think it's a very good idea. I think "ideally" the site should probably have 4 bankrolls, one for 0.5x, 1x, 2x and 4x. (and then combine them into 1 "virtualized" bankroll). And allow people to invest into any leveraged bankroll they want. I think combined with offsite, it would be a pretty ideal system.
I'm definitely for being able to choose the max kelly risk. The only thing keeping me from investing into the site is the crazy amount of potential volatility when a whale/whales bets for max profit (as many have seen with that multi account mega whale). There are huge potential swings in the bankroll that can occur at 1.5x kelly and even at 1x kelly. I would personally like to invest at 0.5x kelly and I'm sure many investors probably feel the same.
Also I think a per game max profit of 0.5x, 1x, and 1.5x kelly (current) should be sufficient.
With the current system that isn't necessary. If you have 10% of the bankroll before a bet, you still have 10% of the bankroll after the bet. The only time your percentage share changes is when people invest or divest.
Yes your % share of overall bankroll would change according to the kelly you set. The max profit would also be a variable % of overall bankroll (wouldn't really make a difference to players as they only see the max profit value).