Yes, but ain't nobody really using Jython or IronPython. Yes some people are, but I'd bet a very small group of the greater Python whole. You also introduce incompatibilities that way. Perl6 has this in the base implementation, so I don't have to switch to a lesser maintained distribution.
Maybe, but it seems like a bad idea to invest in Python 2 (which is teaching is ended of life) just to get parallelism when there are other programming languages that have great concurrency stories and a bright future. That said, if PyPy3 ditches the GIL, let me know!
Yeah, "not relevant to many people" is a wildly false claim. If it were anywhere near true, we wouldn't see the level of Python 3 support that we have in the major packages (95.8%).