I enjoy GTAO, I play regularly with some chums and we have a great time. I've watched a few videos of streamers playing the actual GTARP servers, but that didn't interest me - it's just a 3D chatroom really. The RP mods don't have any of the cool toys or missions, they're more focused on just player interaction. Things can get really crazy on a regular basis and we all enjoy some casual RP, but ERPing in regular GTAO would just be too weird for me. Most player interaction involves blowing each other up!
ERP has definitely been a thing in WoW since the start, but I've never ventured far into Azeroth. Then of course there's Second Life where it's literally a meme; "Ralph plz go". But personally I'm not interested in ERPing in a MMO, for the same reason I avoid 'sexting' or IM gaming: I prefer a long slow literary exchange rather than a digital face-to-face.