When overlay points to a symlink you get the following message:
!!! Invalid PORTDIR_OVERLAY (not a dir): '/usr/local/ase-portage'
Please modify ./pym/portage.py so that overlay can be symlinks too.
Not sure if just extending the check wouldn't break something else. Path handling is known to be fragile when it comes to symlinks.
It should work as long as the target of the symlink is an existing directory.
Well... It used to not work...
But in the latest portage it works... Checked.