This organization is trying to take up in doing maintenance on the Continental Divide Trail, from where CDTA left off, at least in Colorado: http://www.voc.org/
My concern is that if these long trails don't receive any care they will just disappear. Especially the CDT, which is said to be the most difficult of the three most famous long trails, (CDT, PCT, AT) due to logistics problems. I know there are a lot of long trails nowadays, but a lot of them are not actually complete. CDT is actually not complete either, but CDTA was working on it, before they folded.
I guess if the interest in having long trails, or specifically, in having the CDT, is not there, then maybe it's not an issue that portions of it become overgrown and disappear? If people don't want it, it is not going to be there any more.