Well. This is a lot to unpack but one thing sticks out. You apparently have some type of business renting out Marriott timeshares for other owners, yes? I'm assuming so because you specifically mention a "client" who owns 60,000 Abound Points and a "client" who owns a Grand Residence fractional, both of whom are elderly and have gigantic MF's obligations. In your business do you broker Abound Points for your clients, meaning you might be one of the people being targeted by MVW with this 20,000-point cap on transfers into your account?
The reason I ask is because both you and these particular clients still have other working options if they want to continue to hire your services. This 20,000 cap has nothing to do with transfers or rentals OUT of owners accounts, so their ownerships can still be used to secure reservations from Marriott that you could broker as rentals. I get it, points transactions are so much easier with less fuss and more opportunity for an owner/broker to scour availability on a routine basis, but this cap doesn't signal the end of owner rentals. (It might be the first of a drip-drip-drip that eventually will significantly impact owners' rental rights, sure, but it isn't that now.)
I'm also wondering if your clients have contacted
MVC Exit Specialists to try to offload their ownerships, or, if they've explored the external resale market. They and their families don't use their ownerships and they're obligated to pay the MF's regardless of whether they're able to monetize their ownerships to cover or exceed the MF's. In that situation I'd be more inclined to want to get out than to work with a rental broker.
As for all the rest of your post the facts are that MVW has practically unfettered opportunity to monetize intervals which they own/obtain through means that are stipulated in the governing docs, that the owners' rights to monetize their ownerships are/can be limited if MVW determines to enforce a purposely vaguely-worded restriction on "commercial activity," and, that owners choose for themselves if there's worth/value in any of the offered usage. Regardless of the costs to us, the profit to them or whether any of it is fair, as long as they're in conformance with the governing docs then IMO the owners wouldn't stand a chance of prevailing in a class action suit like the one you mention. Besides which, most of the information we'd need to prove a charge that they're unlawfully/unethically making profane profits off of our ownerships would need to be furnished to us by MVW. There's no chance they'll give it up easily if they don't have to, and they'd bury us in legal procedures/objections right up until a Court would be unable to order them any additional relief. No timeshare is worth that waste of time and energy, IMO.