Left by Rawhide

+1. It sounds like Gentoo would fit the bill for what you need quite well. The unstable Gentoo tree gets very new stuff, but there are a lot of people who actually run the unstable tree (including many of the devs), so I doubt most things would remain broken that long. As others noted, it's also relatively easy to run a stable tree (which should still be relatively modern), with granular settings to decide what you want to pick up from the unstable tree.