For me, it's acceptable if the thread was a discussion or a feature request that has now been announced as being implemented.

A thread on, "will we ever be able to visit other data centers?" was perfectly appropriate to necro when it was announced we'd be getting that feature at Fanfest. Same with "Will we ever get an Oceania data center?"

But a lot of the threads that are getting necro'd are NOT getting brought back up because of news regarding the subject, or the absence of that news. It's one person finding a thread that was controversial when it was added to begin with, and then putting in a troll post to bait people into arguing about the topic all over again.

Edit: Seems CKNovel and I disagree on when it's okay!