The GRASS GIS 7.8.0 was released 2019-09-06, according to https://trac.osgeo.org/grass/wiki/Release/7.8.0-News . Here is an ebuild for that version, along with a patch that fixes a small mistake in one of the upstream files. This is not a mere version bump of the ebuild for versions 7.4 and 7.6. Rather, this drops support for Python 2.x, and upstream says they rewrote the whole package to work correctly with Python 3.x. This ebuild fixes several paths in files from upstream, improving upon and makes grass.pc (the pkg-config module) usable again. It also makes the attachment I uploaded to bug 682188 obsolete (because that ebuild doesn't correct paths, which make grass78 unusable by default after install).
Created attachment 589590 [details] grass-7.8.0.ebuild Ebuild for the new GRASS 7.8.0 release. Works with current gentoo repo.
Created attachment 589592 [details, diff] Fixes python executable name in GRASS build system
*** This bug has been marked as a duplicate of bug 682188 ***