3. seems particularly unfeasible

2. tried, they weren't particularly interested

1. seems nice, though it's a pity that it will break on any manifest change.

This is what the afni authors had to say on versioning 

"We actually use the build date as a version, since 
CVS did not do the versioning the way we hoped. We 
usually ask for the 2 lines from "afni -ver" for it. 
Alternatively, "afni_history 1", shows the last change." (from here http://afni.nimh.nih.gov/afni/community/board/read.php?1,142446,142526#msg-142526 ) - can't we use that to get some manifest-change-resistant live ebuild?

Also, why do oyu minf it being in src_unpack() that way? I actually got the suggestion from some gentoo devs.