29er downhill bike? that's it, the 26" is dead.
but seriously....cool looking bike.
the problem with a down hill 29er is you get the worst of both worlds...the heavyness of the downhill with the sluggishness of the 29er. it will never make it.
a 29er works great with 130mm fork and down...a huge fork with 29" wheels....i don't see it as anything anyone would want.
a 650b however, makes sense. you get a larger wheel, but not that much larger (650 b is closer to a 26 than a 29, it's like 1" bigger) and it's still agile and maneuverable.