I'm partially replicating and expanding on my 2015-06-24 bounty remarks here because you can't find bounty remarks anywhere once the bounty expires and I don't want my very good justification for why this change needs to be made to vanish. So:
Some anime have really long names. And most of the tags on Anime.SE are names of anime, so we would like to be able to have long tags that match the long names with as much fidelity as possible.
We have had far too many meta discussions (one, two, three, four, five, six, to name just a few) driven by the fact that we're limited to 25-character tags. Usually, we end up having to compromise by picking something that isn't really the anime's name, but rather just something sort of vaguely similar with some of the same words.
But this causes problems because it makes it harder for new, low-rep (<150) users to find any tag that is valid for their question (we do not use genre tags like "scifi" or "action" or whatnot). We suspect this just makes them leave the site without asking their question (best case, they find the "retag" workaround; but if they don't, well, crud). This is obviously bad.
So I've been implementing this really ugly workaround where we make parts of names into tag synonyms. But this requires moderator intervention, and is, again, ugly as sin.
All in all, the current state of affairs kind of sucks and everything would just be better if we upped the tag length limit to 100 characters1 or something else respectably long (or maybe made it per-site-configurable if having a higher tag length limit would cause issues [e.g. with performance or with crud] on high-traffic sites like SO).
If this is impossible, a brief explanation of why (e.g. "we cannot make tags longer because that would foobar half our tables and require us to spend 6-8 years unquxing this part of our codebase") would sure be nice.
By analogy: wouldn't Stack Overflow be kind of a pain in the butt if the tag length limit was 5 characters, meaning that we couldn't have good tags for Python, Haskell, Scheme, INTERCAL, Fortran, Erlang, Pascal, Groovy, or ActionScript? Yeah, it kind of would, and that's a lot like the situation we face on sites like Anime.SE now - anime titles are the "programming language tags" of our site, and it just so happens that anime shows (and video games, and movies, and...) tend to have longer titles than programming languages.
1 The suggestion of specifically 100 characters is semi-arbitrary, but I would like to note that we do average somewhere around 1 show per quarter whose full and proper name exceeds 50 characters, so something above 50 would be best for us (perhaps 75, if we want a nice round number). Yes, it's ridiculous that titles are so long, and yes, I think the anime industry needs to tone this nonsense down, but for now, it is what it is.