Everyone can decide for themselves when it isn't worth their personal effort anymore, and then freeze their source checkout right before then.
@
J.C.,
In the meantime (because I may end up writing more advanced instructions), the simple isxp disabling *should* work fine using calibre 2.20,and checking out commit e07fc77a529b1787e9de6210d3e1b56d7569ed27.
Or disabling default programs as I wrote above, based off of commit ff82ba858ca507be263a4cd76495c4c41587a47a.