Large trees won't look handicapped anymore, and dinnerbone was done with all the bugs he was assigned to fix in the current version anyway
Seriously though think about it, even if the logic aspect was figured out (assuming it's as complicated as he claimed) an animation for a falling tree would look weird as hell in Minecraft and it'd look even worse if it just suddenly appeared on the ground
Having "realistic trees" is really the least of our worries about the game right now