Since we are here ... I'd still like to see some way to adopt latest python version if user wants to. One way it could work is that we add a "LATEST" to PYTHON_TARGETS that would always build against best version of python. To avoid complications if a new version of python is emerged together with other packages it must always include also a numeric version like 3_8
Regarding your proposal getting rid of PYTHON_SINGLE_TARGET would be nice but being able to have multiple version of python installed is nicer and differentiate gentoo from most other distro Alternative 2 is also nice, the only thing that make me dubious is that it looks like it will be a gigantic work, but you have a better sense of the situation and will be one of those doing the actual work, so go for it!
