I keep hearing people claim that distribution folks are saying "ick", but I haven't heard any technical reasons besides, "Moving spool directories is hard". When I and others have pointed out that moving the spool directory isn't required; just a symlink, I have heard dead silence. So the lack of technical discussion, but just a stony-silence "No!" is rather disappointing as far as I'm concerned.
I think we should require that new applications use /var/mail, and that backwards compatibility symlinks should exist. If we must back out /var/mail (for no good technical reason that I can determine), then at the very least I think we should state that there that for all compliant distributions, /var/mail *MUST* be a valid way of reaching the spool directory (i.e., there should be a symlink there, or where the spool directory actually lives) and that it be permissible for applications to use /var/mail to find the mail directory (but that applications that want to keep using /var/spool/mail would not be considered obsolete). At least that way applications that want to use the same dirctory as the vast majority of other Unix systems will work without needing a special case for Linux. However, I would much rather see us adopt the full, correct solution, rather than this half-measure. - Ted