I was thrilled by this news but it's going to be completely unaffordable for us. We have 29 users and 51 external collaborators. We have recently upgraded to the Platinum plan ($2460/yr), but switching to the new user plan would raise the bill beyond affordable for us ($8k+ per year).
I think it is a big mistake to bill for external collaborators, it completely screws software houses that need this model to use GitHub.