I couldn't see anything on the botcon facebook or twitter, so I don't know if this is true (because you can't go back into this new registration program to see what is sold out)... but one person claims that 3 hours after registration started, they had sold out of the Thursday Custom Class and the Friday Welker tickets.

If true, it is expected, as the Thursday class sold out first last year (ever since they started selling the unpainted figures, people weren't as keen to be in the Wednesday class to be the first to get the toy)... while the Friday Welker tickets would be the better option, as you are less likely to miss out on any panels on Friday, as they only have them in the morning (the Dealer Room opens in the afternoon), and the Hasbro panel is not going to be on Friday either... but often is on Saturday.

I am surprised that the Welker tickets sold out so fast (if this is true)... but I guess if you are someone who wants a Megatron toy signed by him, this was the only option, and they only have about 100 VIP passes for each day (I recall them saying that it would be a little over 200 in total).

What I'm not surprised about, is not selling out on the first day... or even any mention about how well they did on the first day like they usually say in past years.
And the first day is when they do most of their business, even if this wasn't a last minute start - if they don't get at least half of their attendee packs sold on the first day, they aren't likely to sell out at all.
As they've said before at their BotCon panels, the first day of any of their items (toys & Con) is where they hope to sell out... because after that, it is a struggle to sell what's left.

It should mean a lot of non-attendee sets for the rest of you who wants one.