As one of my four talks at FOSDEM, I gave one on Gentoo titled “Package management and creation in Gentoo Linux.” The basic idea was, what could packagers and developers of other, non-Gentoo distros learn from Gentoo’s packaging format and how it’s iterated on that format multiple times over the years. It’s got some slides but the interesting part is where we run through actual ebuilds to see how they’ve changed as we’ve advanced through EAPIs (Ebuild APIs), starting at 16:39.
If you click through to YouTube, the larger (but not fullscreen) version seems to be the easiest to read.
It was scaled from 720×576 to a 480p video, so if you find it too hard to read the code, you can view the original WebM here.
Striving for greatness 
Your EAPI 2 slide has a slight issue: the line that says “[?flag=]” should read “[!flag=]”