From my experience, I encountered numerous times forms on websites that had ridiculously and arbitrarily short character limits.
Especially on companies’ or administrations’ websites. Kind of as if they didn’t really want to read a detailed message, request, or complaint from customers or anyone concerned by their services… 
Though I admit that in my everyday life, I usually don’t encounter issue with long links (and it’s hard to call a Discourse link a “long” link, they don’t have endless query parameters).
It could be a good candidate for, I suppose, a fairly easy theme component.