Would anyone object if I just deleted this functionality, so people could use templates like for everything else? Or would that be a little too drastic? As a historical thing, this stuff was introduced well before templates, I believe, and was subsequently obsoleted by them.
I'm sure somebody somewhere would object. At the very least, you should run a bot over the WMF wikis switching any use of the feature to templates. Better yet, provide a conversion script so anyone can run it when updating their installations.