In time interest will wane. It may not happen until after this line ends, but I wouldn't be surprised if that happens within the next couple/few years. And whenever that happens, shortly there after we will likely have at least a decent amount of what I call "collection dumpers".... the people who will get rid of their collections after the line ends mostly for at least one of two possible reasons...
1. Feeling their collection is "incomplete".
Maybe some vintage figures (whether it be MOTU, POP, and/or NA) never get released that some people really want and feel that their collection isn't complete. This happened with the 200X line, with a lot of people dumping their collections when it ended. But this doesn't necessarily only have to be limited to vintage figures. Since this line as been "all inclusive" and things like Filmation rights are on the table, in addition to mini comics, etc, some people may get upset if some character that only appeared in one mini comic or one cartoon episode that they really like never gets made, and consider it incomplete as a result.
2. Having nothing more to add to their collection
I know this may seem similar to the reason above, but it is kind of different. It's not so much that people feel their collection is "incomplete" because of a specific character being missing from it. It's just that for them, part of the "fun" of their collection is the process of building it. When there's nothing left to "build", they tire of it. It doesn't matter if each and every character from all previous toy lines, all background characters from all cartoons, comics etc. comes out. Once there's nothing more to add, they will get 'bored' with it. And so some of these people will likely dump their collections as well.
We saw all of this happen with the 200X line after it ended. And many figures that were at one time commanding high prices really dropped in value.
I'm sure there a few MOTUC figures that due to their combined popularity and scarcity (i.e. Shadow Weaver) may hold more of a value in the long run. But I don't see Fang Man, for example, doing the same. He has a following, but he's not THAT popular of a character. Right now the price gouging on him is due to the fact that he's essentially a sub exclusive now, and non-subscribers can't easily get him.