not sure this is a good idea. on the one hand limiting access will be great for new players and new GMs alike, but on the other hand, based on my experience with LFR, adding more replay will make it harder to get people to GM. I'm also not thrilled with the concept of having to have a second character on the fly. Show up to play a 5-9 or 7-11 and find out one of the players signed up with his core PCs because he's replaying? and you don't have a CORE pc of the correct level? so now you're playing a pregen or nothing?
this is going to make organizing signups more complicated.
I still miss the Core/Metaregional/Regional scenario system of Living Greyhawk.
Imagine the Core scenarios would be PFS missions, Regional and metaregional games would be "day job"/outside/faction-focused adventuring...