I probably should have linked to the PEP in my comment, because you're right, it says right in the PEP it can change in the future. I would just expect the PEP to change before package managers.

I would think it would be confusing to install a package called "python" and have to run a binary called "python3" while a package called "python@2" installs a "python" binary. But anyone learning Python in the foreseeable future will have to deal with 2v3, anyway. Personally, I'm more likely to reach for Homebrew to install Python3 since macOS ships with 2.7. However, if macOS does ship Python3 I'll probably reach for Homebrew for Python 2.7.