I don't see it damaging 4E now, because they've had a couple of years to build up their own library of player content. Back when it was just the eight classes in the original PHB with only their original two builds, I feel that a truly open license would have encouraged developers to try to fill in the gaps with the 3E core classes that hadn't been put in the first PHB and equivalents to popular prestige classes and such and of course some players would have jumped on the opportunity to play their favorite classes... if the results were bad, some players might go "Oh, well, I guess we'll have to wait until we get an official Sorcerer or Bard"... but if the class looks cool on paper but breaks the game, I think some people would suspect the game is at fault especially if they don't have a lot of experience with the new version.