I don't know the source of this, but I remember reading that most people who become good at things, by practicing for 10 years or whatever, were intrinsically motivated to do so. It's not a process of "want to be good -> force self to practice -> become good", but more of "want to practice -> become good". Can't remember if this was just conjecture, and I'm not a citeable source myself, but it seems like a more likely story. I know I've heard stories of talented people who got where they are because they spent all day noodling on the guitar, or writing programs, but I've heard less stories about people who didn't really enjoy the practice but forced themselves into it via willpower.
Not to say that "just noodling" is all that the person needed, or that no willpower was required, but that the process might be more intrinsic for the people who are actually going to become great anyway.
Growing up, I found that those who ran on pure extrinsic factors with all discipline and no enjoyment either stopped or were stunted by locally optimal decisions. On the other hand, those who went on to study in university and play professionally seemed to derive the same obsessive enjoyment from their craft as I would a video game.
Do you think these data points further prove your point about emotional maturity? Or is there something more universal, that true success requires a fierce passion?
If you want to play the violin beautifully, you have to practice for 10 years, there's no way around it.
If you want to do important things, you have to train in all sorts of capacities, and put in a lot of sweat.
One of the things that differentiates humans from beasts is that we have at least some sense of higher purpose and many of us derive considerable fulfilment from that.
For the most part, most of our education is necessary - and the ability to focus, to plan, to think beyond just a few steps, to control one's desires and emotions, to concentrate and balance one's life energies - this requires education and maturity.
Yes, it can be stifling in some ways, that's ok, we want our doctors and accountants (mostly) to be small-c conservatives. Others can write Operas.
But none of it comes without a formal journey at least in some capacity.
It's a neat experiment but I think it's hard to determine the results. The novelty of exploration in that context just might not be 'novelty' from the adults perspective. Try trading rewards for truly novel things, like, jumping out of planes, I wonder what the result would be.