I limited this PR to 100% objective changes (I hope).

A few other things to consider:

• Consistent capitalization of NumPy/numpy. Currently it is "Numpy" in the title and numpy/numpy throughout, but there seems to be some preference for "NumPy" when not in teletype.
• Perhaps I am not understanding the ASCII timeline diagram, but I would suggest removing one + from each year. It would make more sense to me if the +/| symbols each represented a month (rather than the visual gap between adjacent symbols representing a month).
• The proposal might need to be reviewed for consistency with CPython's definitions of major, minor, and micro releases. I'm not certain, but it seems that in at least some places in the document "minor" should be "micro", and "release" should be "minor release". In any case, perhaps the meaning of "major", "minor", and "micro" should be defined, or the reader could be referred to https://devguide.python.org/devcycle/.
• "For other dependencies, adopt similar time windows of the same length
  or shorter than 24 months." Does this mean "adopt a time window of 24 months or shorter"?
• I don't understand the last alternative: "You can achieve the same name effect by making the window longer which is easier to explain."

Thanks for drafting this!