In Gentoo, a single ebuild is expected to provide ALL implementations of a python module. So, if an ebuild drops python2.7 support, then all ebuilds that depend on 2.7 support in that ebuild suddenly will have dep failures. This can be tracked down to a design flaw in Gentoo ebuilds where this format is used for deps:

RDEPEND="dev-python/somemodule[$PYTHON_USEDEP]"

This should be replaced with:

RDEPEND="$(betterfunc dev-python/somemodule)"

This will expand to:

RDEPEND="python_targets_python2.7? ( somemodule[python_targets_python2.7) python_targets_python3.7? ( somemodule[python_targets_python3.7)"

This will allow MULTIPLE, SLOTTED versions of python modules to satisfy depdencies, so that if somemodule 3.0 is the last version with python2.7 support, it can be installed alongside somemodule 4.0.