Such a change would only benefit the early investors insomuch as they already reaped the greater reward. It wouldn't give additional benefit to early investors on an ongoing basis (like how AM IPO holders have an enormous advantage due to 35x rise in share price making a larger barrier to entry for new investors on an absolute basis), because as the way it's set up, all just-dice investors will always share equally in benefit on each roll, proportional to the amount risked into the site bankroll. The longer you hold, the more the benefit is compounded. There's really no way to give a benefit to early investors at the expense of newer investors without some sort of literal bonus applied to accounts with an ID number smaller than {insert arbitrary cutoff here}. And that will do nothing except deter newer investors from coming in, which is bad - investors should want more investors to come in, because if the winning pool is large enough, it will encourage larger bets. Since all investors share equally in the profits of each bet proportionally to the amount bankrolled, it's a net win for all investors. Granted, you're not going to make much if you only hold .001% of the pool, since the pool size is variable, but over time it's better for everyone to have a large bankroll to attract larger bets. And everyone knows that the high rollers are what makes a casino profitable... basically, a big payout pool will result in a positive feedback loop, generating higher payouts attracting higher bets, while simultaneously generating higher losses and therefore higher fees for investors.

I've been toying with a concept of a gambling site that allows direct investing, but this is a MUCH more elegant solution than what I had in mind. Really, really brilliant implementation.