To point number 1, I tend to think of flow as helpful but not necessary. For some tasks, I'm not really sure flow applies at all. I mean, I'm pretty damn good at tying my shoes. I do it without even thinking about it. I don't think flow was involved in learning that; it's just muscle memory. That's a trivial example of course, but there are other factors than flow which influence the effectiveness of practice. I don't think we should just give up if we can't have flow.

To point 2, you're right of course, but we can't be world-class at more than 1 or 2 things anyway. There's still benefit to being pretty good at something. A great phrase I stole from a blog called All Japanese All The Time is "You can have, do or be anything, but you can't have, do and be everything." If you want to commit your whole life to being say... the greatest chainsaw juggler in history, that's probably achievable. But you aren't also going to be fluent in 10 languages, an expert computer programmer, a world-class guitarist, and a grandmaster in chess.

I'm alright with only being an expert in things I'm able to devote full-time efforts to. But I'd also like to be pretty good in other stuff. How can I take bits and pieces of time here and there to achieve that? That's what I'd like to see some research (formal or informal) on.