I’m all for documenting and only recommending the use of a “system” Python 2 version. Using Python 3 and/or third party packing of Python (like Anaconda) should be considered exotic and will require additional steps, which the community can provide as there is demand for it.
As the Python 3 story improves for ROS 1 we can just link to the documentation about how to use it.
In any case, I’m all for raising the visibility of the issue in the installation documentation and the tutorials.
Is anyone interested in volunteering to lead the effort? I’m happy to review changes to the documentation and/or facilitate in any way that I can (giving access, reviewing changes, etc…), but realistically if I offer to do it we may all be waiting a long time for me to get around to it. 
Also we should wait to hear form some others on the core ROS team.