Hi,

In case you aren't familiar with FEATURES=userpriv, here's the
description from the make.conf(5) man page:

  Allow portage to drop root privileges and compile packages as
  portage:portage without a sandbox (unless usersandbox is also used).

The rationale for having the separate "usersandbox" setting, to enable
use of sys-apps/sandbox, is that people who enable userpriv sometimes
prefer to have sandbox disabled in order to slightly improve
performance. However, I would recommend to enable usersandbox by
default, for the purpose of logging sandbox violations.

Note that ebuilds can set RESTRICT="userpriv" if they require superuser
privileges during any of the src_* phases that userpriv affects.

I've been using FEATURES="userpriv usersandbox" for years, and I don't
remember experiencing any problems because of it, so I think that it
would be reasonable to have it enabled by default. Objections?
-- 
Thanks,
Zac