There are some en:Wikipedia: space pages that are
now redirects to the
equivalent on meta: . That's all I can think of.
I confess I have in the distant past used the feature for both cases
you two describe. However I came to realize that the downsides
outweigh the ups (even without this annoying new trend in vandalism),
and strongly support turning off the feature.
Minimal "soft redirects" that say "this page is now on meta", or
"please see my user page on en" are definitely to be prefered.
I admit to my own sense of annoyance when I want to see what an
otherwise unknown and perhaps questionable user is up to on Wiktionary
or Wikisource, and I'm redirected to another project. I can find a
workaround to see his list of edits in the project that concerns me, but
it's still annoying.
I don't mind posting to his user page on the other project, but if I'm
asking a question that affects Wiktionary I would prefer for his
response to me to be on Wiktionary.