There are at least 2000 x 2000 contracts in EMini during regular trading hours. Personally I think problems would arise using strategies that utilized .25 tick and had to switch to a smaller one. This would obviously be most apparent in smaller timeframes.
Why don't they merge the S&P 500 pit with the emini. For example, change the quarter tick to dimes, and double the contract size to accommodate both players. So instead of a $50 or $250 multiplier, we could have $100. Volume in the ES has been declining/flatlining since 2008. We need some sort of change in the contract to bring more volume back in. The smaller the tick, the more arb, the more opportunity, therefore more volume. VOTE!
I certainly would favor that, but thinking most small traders prefer the $500 margin. I liked it better in good old days where each nickel was $25.