Keep in mind that they originally required payment via a "special assessment" for the owner to receive the benefits of extending the ground lease, and threatened to place a lien against owners who did not pay and did not sign the quitclaim. How would contract law normally view a requirement to sign over your rights via quitclaim without compensation?
This ground has been covered in threads before that OKW was a test case. Most of us - like me - bought in expecting the contract to expire in 2042 and didn't want the extension and therefore, didn't dig into the contracts to see if Disney had the right to do the extension or not. I would bet well over 95% of OKW owners were fine with ending in 2042 or paying up, and had no interest in picking a fight with Disney.
I don't know how large you think "a substantial fraction of owners" would be, but I think it's only a handful at this point who haven't paid or signed the quitclaim. I think Disney can ride it out and allow a few owners to keep a free extension in OKW's case if they are still around in 2042. I do think at this point that if Disney's lawyers had a leg to stand on, they wouldn't have given up as they did.
But for the newbies who have heard about OKW's extension and thought, "Hey, that would be cool if they extended Beach Club..." this is a big reason why it won't happen. The contract language should be the same for BWV and BCV as for OKW...and more BCV and BWV owners have heard about the OKW owners who didn't sign their quitclaim (or would hear via the internet if an extension were announced). So if DVC did try to extend, I really think a substantial fraction of BCV owners (25% to 50%) would dig in and try to keep the extension for free.
(It doesn't help the arguments for extensions that BWV has cheap point charts that can only be reworked through a new ground lease and the new RIV resale restrictions can only be applied to BCV/BWV/BRV with a new ground lease...and with a mention of RIV's resale restrictions, we should be back on the rails for the thread topic in general.)