git remote vs. submodules

Hello All,
I was just reading about git remote and I started thinking to myself,
"Gee, nothing I've read says that the remotes have to share a common
ancestor.  I wonder what would happen if I added two independent
repositories as remotes to a superproject?"

So I tried it in a very trivial case.  The first thing I learned was
that I need to make the subprojects subdirectories of a top level
.git-housing directory.  Or else, when I merge them in, everything in
the top level of subproject1 gets mixed in with everything in the top
level of subproject2.  So this doesn't seem to be a good solution for
marrying arbitrary subprojects together.  But if I set up a library of
subprojects properly, it seems like I could do this.

So now I'm wondering... has anybody else ever had thoughts along these
lines?  Has anybody tried this?  Has anybody seen it work (or fail
miserably)?

Why would I want to do this instead of using submodules?  I dunno.  It
just came to mind when I started trying to understand what's really
going on with remotes.  And I vaguely (and perhaps even correctly)
recall there being some controversy regarding submodules when they
were first introduced.

Anyway, I figured It wouldn't hurt to ask folks in the know.

--wpd