Are you talking 2042 resorts or the ones that are expiring later?
2042 resorts will fall in value as they only have a few years left on them.
As for the newer ones,
@stewart715 kinda nails it, but I think you really have to highlight the restrictions aspect. We do not even know how Riviera is going to go over in the resale market.
I do not know what will come after Reflections, but I am sure Disney will have something, so I think there will still be a decent amount of resorts to switch into.
Lack of resorts to switch into will hurt Direct sales more, imo, because Disney touts that as a selling point, while those of us in the know, realize it isnt exactly that simple. Disney doesn't really inform people that switching at the 7 month window can very hard, or even virtually impossible. However, I bet in 2040, Disney fails to mention that in 2 years you will not be able to switch into OKW, BWV, BCV, VBR, HHI, VB to their direct customers!
Hopefully I will have a better answer as 2042 approaches, and I am semi-retired and piloting the monorail.