Like Herdmeister explained above, no new additional seats will be available for sale. 123 will become a student section. They're just swapping seats.
That being said, I like the move. I like it because the Marching Thunder and the Maniacs, as student organizations, should be the heart of the student section. As they were in the endzone they were separate from their classmates. As it will be in 2016 they'll be flanked on either side and from above by their fellow students.
Having students in 123 expands the student section to cover basically half of the south endzone. That southeast corner is going to be a madhouse. I think it will make the student section look a lot bigger too. I think the Maniacs that usually occupy 117 will be in the position to see a lot more camera time in 123.