By gating the first level or two of PPs behind NPCs for a few events seems like the best plan overall; PCs can request specific PPs, Plot can send out NPCs to teach them, and then balance around just a few PPs at a time (and hopefully send out some mods to make the PPs really shine while they work on getting the next ones out to PCs).
Given the challenges that plot teams already face with executing content, adding a structure that requires plot to manage skill release and characters' access to build expenditures is deliberately placing itself at risk of encountering a significant number of points of failure. Plot resources are typically strained, and many plot teams encounter levels of turnover that must be managed and resources dedicated to onboarding new members. This, in addition to executing the content of the weekend, accommodating the natural unpredictability of players, providing accessibility for the players' diverse schedules and availabilities, and tracking the status of nearly two dozen Paragon Paths worth of progression, puts an unreasonable burden on plot teams. Failure to deliver here compromises the customer experience on a vast number of levels, as challenges cascade and further complicate matters. Even if this works for every plot team but one, that one failure is unacceptable and unnecessary, as it was an entirely avoidable situation from the beginning.
Paragon Paths should not need to be slowly introduced for balancing. If chapters are properly conducting playtests, and are provided adequate time to do so thoroughly and collect meaningful data, then the Paragons should be released as a balanced end product. If owners are taking serious, objective looks at the data, and making sound decisions based on player feedback, then no gatekeeping should be necessary. Gatekeeping these abilities demonstrates a failure of the playtesting process, which would be even more concerning given the potential systemwide collateral damage that such failings would suggest.
The risks to such structures are far too extensive. The rewards either already exist or do not require these structures to be accessed by those who value them. The foundations are concerning, and are symptomatic of greater system failure. The detriments are unnecessary, inevitable, and unjustified. These structures do nothing to uniquely enrich the customer experience, and only serve to burden and complicate the lives of both plot teams and players alike.