again, you are starting from a mistaken premise. /usr/portage makes sense, when you consider its history. It may not be the appropriate decision, but with its background it was logical back then.
And if something is not broken, don't change it. You do not know what old tool/setting/whatever might suffocate. PORTDIR is not a mere workaround. If you are sure that there is no old crap lingering around that might expect portdir as /usr/portage, use it. Besides /usr/src/ contains linux and other sources. Wrong too? It is f* tradition. portage does not contain temporary data or database stuff - that crap is in /var/db, /var/tmp/portage, /var/lib. So the worst stuff is somewhere already.
