One potential drawback is that it's sometimes hard to have "performance enhancements" as modular add-ons; and thus some code may be basically forked between free and enterprise versions. So it is possible that trying to apply some improvements only in enterprise version can cause sort of artificial complexity (or maintenance costs). But that is probably the price to pay for being able to have different-enough versions -- in a funny way, it means enterprise version users may end up paying more for the privilege of having the privilege.