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.