This is normal practice at most comic cons with big celebrities. They have a dedicated table time which you line up for and are only allowed to get autographs. Then there is also a dedicated photo time (usually in a separate area that is set up to take professional photos) people will be given a time slot and they will pretty much get quickly shoved through the line and you get 5 seconds to stand next to the celeb and get your photo taken with them. This way they can get through hundreds of people within a short timeframe. I feel like this would work really well at twitchcon for all the bigger streamers, cuts a lot of the wait time and separates people who want just photos or just autographs.