It would definitely take a significant hit, both on the raiding side and the casual RP side.

I know people who only play this game because its modding scene is so easy to get into, and I know hardcore raiders who say that if they couldn't use some key plugin that makes the game more functional they would probably stop raiding. While its not a majority of players, it isn't an insignificant ammount either.

I honestly think SE has more to lose than gain by going scorched earth on plugins or mods.