With the popularity of race conditions involving /tmp and such, would
the idea of a per-user temporary storage space be helpful?

I was thinking of modifying the memory filesystem to do some magic
based on the user using /tmp.

Root would have full access to tmp, via /tmp/all/
Any user can put things in /tmp/common/ which would be "shared" just like
/tmp is now.
Accessing simply /tmp would make a special location just for that user,
where files placed there are not accessable by the other users.

Has anyone tried something like this, or will this break too many things?

If one was clever /tmp could even automatically expire based on userid
and last access time, perhaps.

--Michael