OK, so here are my wild-eyed predictions, such as they are, grain of salt, all that crap...
After 2042, Disney will assume the responsibility for the maintenance fees for the points it now owns. They won't try to pass it off to the remaining owners and I don't think legally they could. Just because fewer people own points overall as of 2043, that doesn't mean those that own suddenly own more. If DVC at that point controls 85% of the points, they assume 85% of the maintenance fees.
But unlike DVC members, they won't be beholden to the rule that you can't use points as a money making venture. After all, had they never offered the extension, then once they had control of 100% of the points, they could choose to make it a regular "cash" resort, couldn't they? Someone please let me know if I'm wrong. As I often say, it won't even be the first time I'm wrong today, let alone ever.
Now here's theory #1 - Old Key West becomes the DVC equivalent of the promotional offer other timeshare companies inundate your spam box with (or your fax if you still have one because you're a lawyer and/or old
) When guests book a week anywhere else, they'll get an offer to extend their trip for an extra 3 nights at a studio OKW for "only" $X. What that price will be will depend on what rooms in deluxe or DVC resorts go for at that point in the future. And you'll be able to upgrade to 1BR/2BR/Grand Villas based on availability. But it'll only be for 3 nights. AND it will be contingent on the adults sitting in on a pitch for whatever the newest DVC resort will be, but maybe you'll get freebies like those extra days on your park tickets, or tix for the waterparks or fastpasses etc.
Meanwhile, if it's at all legal, DVC will go to the remaining owners, those who extended, and entice them to relinquish the remaining ownership in their points so they can raze and rebuild, much like a developer offering above market value to homes on a block he'd like to convert into a condo or something. If they don't offer the $25per point back, maybe offer a partial buy back and a swap for other DVC points they have in stock, even if they expire before 2057.
If they can't do that, then you'll see a disproportionate amount on overbooking at the Values and Mods so they can give guests a "complimentary upgrade" to OKW. Or they'll do that anyway until they're in a position to raze and rebuild. After all, as much as they'd like to profit from the rooms, as long as they break even with the maintenance fees they'll have to shell out to themselves, they're not that much worse off than they would be anyway if it remained a DVC resort as it currently is. And if booking All-Star resorts at 120% occupancy so they can take the overspill and move them into larger digs and shift that money for the rooms, "on paper" to OKW, it all balances out.
The only potential downside is if guests start to get the impression, earned or not, that OKW is a pit because it's so old. Even keeping up with the maintenance might not salvage the rep that it's an old resort. But at that point many of the resorts we know and maybe love will be even older, so who knows if that will be an issue. There will be complaints about location, but is it really that much worse off than most of the Values? You're still a boat ride to Disney Springs.
So that's my take on it. I wouldn't bet money it, but that's because I'm a DVC member and therefore, cash-poor