I've read somewhere in the 5 - 6 thousand ticket range. We've been there in 'High Season' when it's crowded and never been shut out. Buy your vouchers when you check in .
I've also read that the limit is rumored to be 5,000; however, I have experienced an e-ride night which was fairly crowded and I counted more than 5,000 people. Okay, maybe I counted a few people twice....
I didn't really count, but there had to be more than 5,000 in the MK that night. Maybe the cheerleading groups there that night didn't count against the E-ride limit. We had many wait times of 20 minutes or longer.
On all other E-ride nights we have attended, most of the wait times were around 10 minutes or less.
I asked one CM if he knew the limit and he didn't, so that's one CM you don't need to bother asking (I think his name was Fred).