Alright so I am totally onboard with some kind of idea like this! I think with a few tweeks, it could be a really good feature.
This is more up my alley. I love the idea of after a year, a story is autmoatically labeled (on hold) and you can even filter out if they show up in your hot list/search/etc. Kind of like Mature. That way your list is pretty fresh, or filled with completed works.
I think it’s more to help filter out the abandoned stories that are clogging up the tags and search engine. I don’t mind unfinished, but I don’t want one that’s been left behind. It’s just a waste of time to me, since I know it won’t be completed. But I think instead of unpublishing, Kales had a good point that they get flagged as (on hold) and you can then filter them out of your search engines, sort of like with Mature.
I think OP said a year, which I think would be a good time frame.
So again, I think adding an (on hold) filter, along with [COMPLETED] and [Mature] would be awesome, and it gets triggered after the story has been un-updated for a year. And you can set your search/find settings to include or exclude those stories. I have no idea if this would prove to work well in practice, but in theory I think it’s a great way to organize the stories on here, since so many are abandoned.