For what it's worth, the EOL on Natty was almost 2 years ago now:
I'm inclined to do-release-upgrade on that buildbot and simply remove the natty builder, and work on fixing the twistedchecker builder once everything is on supported versions of stuff.
If nobody objects by tomorrow I'll probably just proceed with that, since I don't think it was ever explicitly our intent to support OSes that have been EOL'd by their vendors (except perhaps the unkillable, eternal XP...).
-glyph