It seems weird to me even with the CTE deadline that they would wait until so late in the cycle to accept from the alternate list because the later it gets the more likely it is people from their waitlist will have decided (or had another CTE deadline) to go somewhere else or been accepted off another waitlist. Since they created a 'high alternate list' of folks who interviewed late in the cycle in April, this makes me believe they wanted to accept them outright but because there weren't any spots available they were forced to create this exclusive alternate list. I think there could be some movement but those spots are most likely going to those on the high alternate list.
I've been lurking around some other UC sdns out of curiosity and it seems like there was generally less waitlist movement this year. At UCLA the rumor is they over-accepted and won't pull anyone from the waitlist. Again, I want to remain hopeful for everyone still on Irvine's alternate list, but it seems this year the new traffic rules changed everything haha