A lot of booths barely get the set-up finished in time for the Preview Night Crowds as it is. I was at the con from around noon on Wednesday and it's amazing the transformation that happens from that time to opening. You'd never believe some of the places were going to make it in time.

If they were to make Wednesday a full day then they'd have to make all day Monday and all day Tuesday available for set-up, which starts to get even rougher on folks that are taking days off and leaving behind their brick and mortar businesses to be at the con as it is. As it is SDCC is already the longest convention of it's kind, and in my opinion, it doesn't need to be any longer.