Unfortunatly i'd have to disagree with the idea for two reasons.
The first, being the most important, would be:
1. Why would we need it?I mean we're going to have flying creatures some time in the game?
But I have a comment about that, why couldn't we just put it in first, have it there and then at some point in the game people could be like "Hey we found a new flying creature!Screw hang gliders." Which would work, but I don't think it'll happen.
and the second:
2. There is no second, I just wanted to say I like the idea and that it would be great fun, but the problem is is my first reason. There are going to be flying beasty like things so there are no need for gliders...but you know what people SHOULD discuss, creatures that walk on the ground and you can ride on'em. I see that discussed so little around here.