Thanks, Brett. You've brought good points. And I wasn't necessarily advocating about adding TOML support to stdlib, actually it was more about having a defacto library for TOML parsing. Currently setuptools, pip and others(now even requests) are under supervision(not total but some) of PSF. I suggest doing same for TOML parsing. If we are bringing new standard to python ecosystem we should provide all parts needed for this tool/lib/standard to be usable "out of the box" for most users.
That's unfortunately not a general thing we can make happen. Someone needs to implement a TOML package and then ask to move it to under the PSF after gaining enough traction. Your best option would be to ask one of the TOML package authors if they are interested in moving their project.