I realize Topics are not widely implemented but would love to see this feature for the few lists who do use them. One very non-technical chat list I'm on is almost ten years old and split off of a much older list on the same subject. Last year I helped them move to Mailman from that expensive service whose name I shall not mention.
Not only does this list use Topics (16 at the moment) it also allows, even welcomes pictures and allows a few other types of attachments. However, it is always confusing which Topic to use. Not all attachments are pictures... Bottom line is that no matter what naming schema is used *someone* will get confused and then gets yelled at by the current list owner (not me, I ain't taking the job!) for posting attachments to the wrong Topic. Not only is this embarrassing for the 'yellie', it annoys the rest of the members seeing this same scene play out every few months. Worst of all leads to early list owner burn out and good ones as we all know are rather hard to find.
If message size limits could be set per topic then an impartial reply-bot would get to be the heavy in private. If this would be too code bloating, then having two (or perhaps three) levels of size limits with each Topic being assigned to a level would work just as well.