The initial regulation inn the US was not "all shoes," but rather those with thick soles, iirc. So much for that...
Departing PRG in Czech Republic last week, nobody had to doff shoes iirc, though a few Americans on autpilot did remove their shoes without being asked to. It seems we made it to Heathrow anyway, where everyone had to doff their shoes, even the woman with the very slimline sandals with ultra-thin soles.
Quote appropriate for this post: "Good doggie!" - Ivan Petrovich Pavlov...