The good old pastime is gone. Here is one that is inferior (old questions in bad shape probably aren't very valuable, we didn't ignore questions randomly) and less likely to result in a useful result (the original asker is often gone too, unable to give any clarification or confirmation) and likely mostly helpful for AI (which currently and for the foreseeable future doesn't give attributions). Why don't you do this?
Reading it like that I admit I'm not that bored. I actually want to do something really meaningful. Wading through the long tail of lowly voted, unanswered questions sounds like a Herculean task. Surely some of them are pearls waiting to be polished but most are not. The pearls to sand ratio would probably be most unfortunately, mostly downvoting and closing. Simply deleting them all would be faster.
In my eyes the original mission failed in that activity came to a premature halt and future knowledge will not be contained in the library. Likewise I don't want to be the last one looking through the remains of what is left from the past.
And what would the purpose be? Just to help AI crawl the content better and serve it on other sites without giving any attribution? This is more and more happening and might not be enough motivation for some people. I don't want to be the nameless helper of AI applications.
Nevertheless there are the usual things you can do:
Gamification Give rep and badges for the activities that you want to push. Like the excavator badge only much more so. And edits that add or update content are really badly paid in rep.
Tools Implement (by the company) better tools so that the work can be done more efficiently. That also increases motivation. Like better lists of questions I'm really interested in. More support in finding duplicates. Labels for outdated answers. Or else
Money If the only reason is AI, surely AI companies can pay people to do this work for them. AI is said to massively lower entry possibilities for software engineers, the money saved can be spent on data collection instead.
Statistics Try to gather information about what needs to be done and what is done and visualize it. If only quality could be measured somehow. But surely some quantitative stuff can be given like unvoted upon questions/answers. People like to see their progress.
Collaboration See for example the burnination process where the community coordinates tag removal. The same way for example clean up operations could be coordinated.