Yes, I trained during those decades and at pretty close to that time of night. Continuing to train and compete after I got married and inbetween maternity breaks and while in grad school, my non-skating husband, a musician who liked to rehearse at home late at night himself, was fine with my schedule, except when he got stuck with walking the floor with teething babies night after night . But it's the best time to learn new skills and practice if your bio clock allows it. I've virtually always skated either around midnight or, just for fun after retiring from competition, at noon on weekdays when the rental for private ice was cheapest at neighbourhood rinks. My competitive partner and I were night owls, so that was fine for us.There are coaches in my club who have international pair skating experience.
But there is not appropriate ice time available for interested skaters to work on pair moves.
If they wanted to start a pair program, the biggest challenge would be finding ice time that could be devoted to pair skating (or otherwise sufficiently empty with the few other skaters on the ice able to look out for themselves), at a time of day when the skaters could be available and at a relatively affordable price.
I know a woman who skated pairs in the 1970s, who says they used to practice from about 1:30 to 5 AM.
You're right, most clubs want to limit pairs on the ice from two to, at most, four at a time. The more inexperienced they are, the fewer other skaters there should be around them. The expense for special-purpose ice time is prohibitive for most clubs and skaters, and the availability is scant (especially in a country like Canada where you have hockey wanting ice late at night to accommodate players with day jobs).