As a high school basketball player, this is still a possibility for me (although a faint one). However, I am NOT going to be 6'9. 6'1 at the most. Still, if I grew to be 6'9, I imagine I would model my game after Magic Johnson's and become a match-up nightmare in the post. I would learn the skyhook and a fade-away post J so I could shoot over any PG or SG who was guarding me, and if the other team switched a big man onto me, I would take them out on the perimeter and either blow by or take a Hedo-esque step back J.
As it is, I'm pretty quick and I have a pretty good vertical leap and a well-developed mid-range game, but I can't post anybody to save my life. I have good vision, too, but I need to get my strength up so I can throw longer passes with more accuracy.
I imagine that if I was 6'9 I would have a legitimate opportunity to play in the NBA, simply because the taller you are the less skilled you need to be to make it to the league. I would perfect my crossover (which is already my go-to move) and lift until I was big enough to post and strong enough to get 3's up late in the game without a problem. I would dedicate myself to basketball completely if I had that kind of height--as it stands though, I'm not a uniquely exceptionally athlete and I don't have the size to compensate, so my prospects are looking a little shaky.