vacuum full in the background

hi,

i'm happy wih autovacuum and cluster.
but now I ask myself, why i can't move the last table rows
to the beginning step by step?
vacuum-full needs an exclusive lock.
that is okay for me, but if a query arrives, that is waiting
for my vacuum-full, i would like to save my vacuum-work
and pause.

when there comes an bulk-import, i know that my vacuum
will not modify the contents of the table.
so it would be great, if the import can append to the table
normally.
when my vacuum finishes, it would be great, if the new
free space in the middle could be eliminated by just
modifiing one inode-pointer.

are there reasons, why this could not be done?

regards, maletin.