Just in cocideration, if we were to be able to get Ayumi Hamasaki (which no anime cons has gotten yet), the only way we'd be able to afford her to come, and the equipment neccesary to support one of her shows would be to charge attendees about $150 extra.
Sometimes companies provide support to cover the performance fees and such, but you still have to fly them over, feed them, and house them. And even 1 singer is never alone, they usually travel with an entourage.
Right now I don't see us as having the capabilities to support a J-pop or J-rock artist from Japan. Now, in the future, that's definately a possibility if Kumoricon continues to grow.