I just popped into this thread, and was about to post almost exactly what
@ShinBlanka stated (albeit from a vastly more independent perspective) with regards to why the DLC characters should be allowed.
Basically, if you are going to ban the DLC, you're going to have to ban Ferra/Torr as well. And, you've got to allow Tremor players to imbibe in nootropics/and or compete with CronusMax macro mods.
Incidentally, I am planning on attending anf competing (although I am not a Top Player by any definition, for whatever that is worth). Ordinarily, I would be in favor of waiting a certain period of time before allowing fresh DLC characters to compete, but I am honestly a trillion times more concerned about some previously disregarded Variation of an original cast member coming in with some crazy buffs that were either overlooked and disregarded by the community, or didn't find their way into the patch notes.
We have to let the game ride out somewhere, and this is it. The 18th is only 12 days short of the arbitrary 30 days that many see as the appropriate amount of time to sufficiently scout the game for game-breaking glitches, so let's not pretend that we are so far off schedule that every bad thing that happens at FRC could have been entirely avoided by another 1 1/2 weeks. The first major after a patch this big will always be wild.