I might get away with 48GB (don't know, I have 64 now on my work machine) but I had a lot of swap usage when I was running on 32GB. Some of us do need a lot of ram.
Well, iMacs used to be fairly common in music/video production. Given the move towards more casual use-cases by Apple, I would say there aren't many anymore, but if they were to put pro chips in there, I'm sure there would be more.
I have the feeling most music/video producers these days like the laptop format anyway (a music producer would typically want to have access to his projet in his home studio, live stages and pro studios) and the imac format is getting limited to traditional pro desk use.
With usb-c/thunderbolt, it is hard to be a pro user AND be interested in the iMac form factor when you can have a mobile device that you can easily dock to a large screen and have the conveniency and comfort of both a laptop and a desktop.
Outside of companies that wants fixed, kensington locked desktops for their employees, I don't see who would choose an imac over anything else.
