I would consider Biyombo simply a 4/5. He has the ability/potential to guard inside AND outside as he learns the game. He shouldn't be guarding gigantic , weightier bigs for 35 minutes every night--not until goes through the normal physical-broadening that many 20-somethings do.
I would not quite pronounce the death of the traditional "Center". Howard and Bynum are interior-oriented, massively strong traditional bigs, and anybody would love to have them on their team. Also, Yao Ming should still be in league. Darn those premature injuries.
I would be careful about saying this or that trend is "dying". Trends tend to be cyclical. Also, I heard the international game was set to adopt the nba lane, which should infuse more post play into the overall pool of available players.