PT7 also used 8-character IDs (at least since 7.1). The 8-character size was done just for size considerations (to keep the size of the file manageable). That being said, the IDs just have to be unique so using 36-character IDs should be fine.
EDIT: I was partially wrong. When creating notes for multiple projects (i.e. multi-notes), for some reason those use IDs that are 36-character long. That’s probably a bug/oversight and still happens in 8.0.
I must say that I’m curious why you want to do this.