> > USE=live could perfectly make sense, if it is equipped with
> > the obvious meaning:
> 
> Well, it seems to me that you're trying to shoehorn a USE flag into
> a role that's intended to be filled by package sets.

Maybe there is a misunderstanding:  I am mainly suggesting the "live"
USE flag to allow the user to decide in a uniform manner (and on a
per-package basis) whether new sources shell be fetched regularly
before the rebuild (that's why I said that my suggestion is
slightly OT).

There is no way to do this by package sets.

But *if* a "live" USE flag would be uniformly used for that purpose,
it would have also the "side effect" that you can read from IUSE
whether it is a live package, i.e. there is no need to put this
information additionally into the RESTRICT variable.

> The idea is
> that instead of settings USE flags in package.use, you'd define a
> package set containing the specific packages that you want rebuilt.

I guess this is part of the misunderstanding:
I do not care so much whether @emerge-ebuild would select all packages
with "live" in its IUSE or only those for which the "live" flag is
actually set (from your reply I understand that you would consider
the latter as an inappropriate use; I do not protest. Anyway, even the
*possibility* to do this even if it is not implemented - might be
considered as an additional feature of USE over RESTRICT).
However to repeat:
The main point in introducing the "live" USE flag should be IMHO to
let the user decide whether the sources should be fetched. The fact
that IUSE then marks live ebuilds in the way which you wanted is an
additional side effect.

Regards
Martin