Does it need fixing?: My opinion on this is probably not of much use, but I shall mention it anyway, just in case it might be.
Seeing as most of my reading of the DC Forum is via the Bazqux RSS feed aggregator/reader, I can read what I need reasonably quickly. I'd use the analogy here of reading a highly structured newspaper.
So I rarely read the DC Forum content directly, and thus (Re-)introducing the Ignore Thread feature (I realise it had been discussed, but I hadn't realised, or had forgotten, that it had been implemented and then removed) wouldn't make any difference to me, and I almost certainly wouldn't use it anyway.
When I read something - anything - I don't really worry about whether I won't want to see/digest certain parts of it. It's the potential increase in my understanding of something that counts for me. I can always skim over bits that do not seem to be a constructive use of my cognitive surplus - and I do skim-read like that a lot.
I like to be able to see - albeit briefly - what has been written, because, in my usual state of potential crass ignorance, everyone's input is potentially worthwhile and a potential learning experience for me.
So, if forum members have requested (Re-)introducing the Ignore Thread feature, then why nor re-introduce it? Does it cost anything to do that?
Something that may need fixing: One of the minor frustrations of the new DC Forum regime for me is that, where I had blocked someone from sending me PMs (Personal Messages) under the old regime, their forum posts are now being automatically blocked under the new regime, accompanied by the standard comment "You are ignoring this user", or something - when in fact it was never my intention to block or ignore that user's comments in the DC Forum, but merely to stop them from sending me annoying PMs. What they might write as a post in the DC Forum would continue to be potentially interesting/useful to me and I would prefer to be able to read it by default - i.e., without having to press some special exception button to reveal its content.
As Number 5 put it: "Need more input!", so I do not want my input to be automatically filtered from my view. My brain will perform the necessary analysis and filter, thanks very much. Of course, no two brains will necessarily be alike in this regard.