We have a small one and you can get loads of hot water out of it non stop. I get your idea but I don't think it works for most people, that tank must be kept hot at a price too. IIRC the publicity was that you could get hot water "faster" which is a question of a very little difference if any IMO.
A tankless electric, interesting, why not, we have 220V/32A lines in the kitchen, I wonder how well that would work out.