I can tell you what Gentoo shouldn't do: blame upstream for having assigned themselves the mission to support and test 2^N combinations of options for which they don't get to curate N.

They're free to limit which options they offer, they're free to limit which combinations they support, and they're free to fork or drop the software they offer if they insist on keeping the 2^N purity (which they eventually did). But that's Gentoo's mission, not upstream's. Upstream is just giving them software for free on an as-is basis.