This coming from the perspective of someone who joined in to PFS relatively late (partway through Season 6) and hence still has a lot of scenarios to replay especially from early years, but much of my local lodge is more experienced and has been playing from day 1:
I would like to see the option to replay everything, on the basis that even with some new blood, we'd need some of the more experienced players to fill in tables. I can also see the potential problems with item hunting of unlimited replays. I'd rather see something along the line of time gates. You can only replay a scenario for free after you haven't played it for X years. This will mean you always have scenarios to play, even if you've played them all (unless you're a crazy person who manages to play all 11 years of scenarios in 1-2 years), but can't pick and choose. Admittedly probably a pain to track and manage, though.
Another option I could see is replay if there are new people at the table. So you couldn't have a free replay table of 100% new people, but if you have, say, 2 newbies, vets could fill in to make it a complete table. Like above, this is coming more from the perspective of playing than managing.
Or perhaps free replay but you have to play 20/30/etc games between replays?
TL/DR: I want to see a way to cycle replays so that vets can help fill in open seats at tables with people wanting to play scenarios for the first time, but with some kind of automatic gating system (be it time, games played, etc) to prevent the item and scenario farming problem you see with raw open replay.