It happened before that a developer added an epatch line to a newly-added src_prepare on an ebuild that is using EAPI < 2. While people should test their ebuild I would rather start with the idea that repoman should catch this beforehand.
Created attachment 367838 [details, diff]
Working on this one, sent a patch to the portage-dev list. Attached is an updated version of that patch based on list feedback. Patch also checks for pkg_pretend in EAPI<4.
Pushed a revised version to git, commit 00560e0b22059ffb42d965b4ef625950ab987afc
released in portage-2.2.11