According to this guy, the intent of the provision has nothing to do with the US (or Australia) although the plain language of the article makes it sound like it applies:
"Specifically, in 2008, shortly after the precursor to Article 9 was implemented, FIFA’s Executive Committee issued a
public statement clarifying its rationale for the rule. In the statement, the Committee explained that “[r]esults on the pitch decide whether a club goes up or down a level in every championship around the world except in the United States and Australia, where there are ‘closed’ leagues. Recently it has been possible to achieve promotion artificially by buying or moving a club. FIFA wishes to make sure that this cannot happen again.”
https://medium.com/@terryblaw/does-u-s-soccers-league-set-up-violate-fifa-rules-ceec15f54244
According to a podcast I recently listened to (Total Soccer Show - great show if you've never tried it before), this rule was put in place after / because of an extremely specific situation (in Spain maybe?) in which a long-time owner of Club A (location X, 4th tier) then purchased Club B (location Y, 2nd or 1st tier)... and after owning both teams, instead of working to get Club A promoted, the owner essentially just demolished Club B, and replaced it with Club A (branding, players, etc.), thereby "promoting" Club A without the hassle of actually needing to win anything in the lower tiers to actually get promoted.
This is interesting to me in 2 ways: 1) if there this particular FIFA provision was instituted to prevent an extremely specific scenario then, on the surface, FIFA will probably not intend to apply it to the US in any fashion ... but 2) the purchasing of a club in order to move another club or a new club to a top tier does sound a lot like how MLS expansion is happening.
All that being said, I think this arbitration attempt by Miami FC and Kingston Stockage will go nowhere. First off, the situation in the US is extremely different, because the soccer structure and pyramid are still in its infancy (relative to other soccer nations) and building. Second, and more importantly, FIFA knows damn well that a massive, massive chunk of its revenue comes from the US (viewership, sponsorships, etc.), and there's no chance in hell FIFA pisses off all of the people in the US that have the money, power, influence, etc. (see: USSF and MLS owners) by doing anything about this, at least in the short-term.
IMHO, instituting pro/rel right now would set MLS and soccer in this country back 20 years. Do I think there's a place for it in the long term (15-30 years from now)? Maybe. But I think we need to get MLS fully expanded and get USL fully expanded first (what fully expanded means is anyones guess though). Realistically, I could see NASL dying, USL hitting 40 teams, MLS hitting 32+ teams, and then having something like MLS 1, MLS 2, USL 1, USL 2, NPSL?, and so on... with pro/rel of 1 team each season.