As you might have seen, many packages fail to built or install or run with no threading support in python. I thinnk it is reasonable to force threading in python more strongly. As we already use +threads I would suggest the following, go for package.use.force and see if nothing breaks (which shouldn't) and perhaps later drop the use completely. Any thoughts?
Even python internals are broken without threads (thanks Arfrever digging this out) https://bugs.python.org/issue25364 (errors in over 50 test files), https://bugs.python.org/issue25365 (test_pickle), https://bugs.python.org/issue25366 (test_venv), https://bugs.python.org/issue25367 (test_coroutines), https://bugs.python.org/issue25368 (test_eintr), https://bugs.python.org/issue25369 (test_regrtest)
Sounds good to me.
Threads are enabled by default in 3.6. It is mandatory for building python since version 3.7. Advisory: https://docs.python.org/3/whatsnew/changelog.html#changelog
