A house built in 1987 in Massachusetts didn’t have air ducts as oil heating didn’t require it. Messy as all get out trying to get a heat pump installed. All of those kinds of places (“where a/c wasn’t needed”) suggest the need for replacement housing which is blindingly expensive.
I think we will probably see a lot of minisplit type heat pumps being installed in the coming years. In addition to being easy to retrofit, they have really high efficiency ratings (20+ seer).
You get a better heat pump setup with old water pipe radiators really than electric radiators. A water-water heat pump with a drilled hole. But it is more expansive than air to air heat pumps.
Generally I think with the cheaper ones, you just use the heatpump instead. Without the old pipes.