base.eclass is broken by design and exports src_unpack() in every EAPI, making it hard to work with VCS eclasses and is generally a very bad practice. Please consider dropping the inherit and inlining the necessary logic in cmake-utils_src_prepare(). Dropping EAPI<2 support (it is used just by a few ebuilds) would probably be doable at the same time.
Yes please!
+1
A testing version of this is in the KDE overlay.
July is coming up, I guess the last thing to do is to check if any packages inheriting cmake-utils call base_* without explicitly inheriting.
Committed the change last night.