I realize this is thinking of an MOC in extremely simplistic terms but don’t backlinks serve as an automatic index? Linking to the page of your MOC takes just as much effort as creating a tag or moving something to a folder. If you decide to leave the MOC page blank and only use the backlinks as the index then there isn’t any upkeep to deal with.
Personally, I feel it’s best to build an MOC as you go. I’m starting with a page of links and summaries for each note.
Hopes this helps people who are turned off to MOC because it feels like it would be too much work.