I think it is a very interesting idea. Heads up you can get a much better feel for ranges and the importance of aggression. I still think you need a basic understanding of poker first but I think you could improve more quickly in Headsup. The disadvantage is that if you are tiltprone you could busto yourself much more easily playing HU just because it can be so tilting when you get beat 1 on 1 vs someone who plays bad. Rake is beatable like you say given that these guys play awful from what little I've experimented with HU at the 5s.