Not much?

Assuming there is any sort of PvP, they can simply relegate the Beta players to a different server, (like pretty much every browser "MMO" that's essentially a power race does. Starting off a new server every few weeks so new players stand a chance.)

As for those who have continued logging it to pre-register, they REALLY don't need to worry about. They have no unfair advantage, every single other person could have done the same. For those who didn't it's simply like joining a game shortly after it started.

IMO, the whole issue has been blown massively out of proportion.