From Serhiy in https://mail.python.org/archives/list/python-dev@python.org/thread/QUUBM7DGSXYWBOLZNWOSCQUDALWJIYZF/ :

    The output of "python -h" is 104 lines long now. It was only 51 lines in
    3.6. 35% of it is about the -X option, and 30% about environment
    variables. Also some lines in the -X option description are too long
    (102 columns). Both topics are "advanced" and mostly interested for
    debugging. I suggest to move them out of the main help output.  […]

Guido:

    -X opt : implementation-specific option; use -X help to list options.

    We could also see if we can put the help text for each of the supported -X
    flags in the table defining these flags […]

GvR again:

    --help-env […] prints info about env vars (new flag)


I would enjoy trying to make a patch around next week!