Since you wanted someone to respond to mechanics ideas and not just appearance (I think personal wings look stupid in about 95% of instances, for that record) Let's run down the list:
Quote Originally Posted by Zoner
DoL sky gathering points,
Terrible idea, now the zone designers need to stick in MORE random little floaty bits than necessary to justify the whole concept. Good luck telling where that unspoiled node is, too, since you only get XY coordinates.
Quote Originally Posted by Zoner
flying in new zones,
Which we already have flying mounts to do, which even relatively intelligently can tell when to switch from land to flight. But if I can just fly, why bother with those?
Quote Originally Posted by Zoner
glide from high places in old zones,
Awesome, let's travel old zones in a fashion that lets us totally ignore the zone design AND the scenery. Don't forget that most zones were never designed to be viewed from a perspective off the ground, so now we need to redesign every single one to work with personal flight.
Quote Originally Posted by Zoner
maybe even entire dungeons that flying is part of the mechanics!
Welp, that mob was just a little too low, sorry it killed you. Aerial combat is hard, at best, and the combat of FFXIV is optimized for flat planes for a reason.
Quote Originally Posted by Zoner
stats could be added to the Wings as well as glamors.
Now we need to balance every single piece of content against the possibility that someone has an extra piece of gear on. Also we need multiple sets of wings, plus a new wing for each primal, plus one for each class for each raid tier, plus tomestone versions, and gee, what about one as a veteran reward?

Flying is rarely executed well, and flying in areas not built for it is just a recipe for disaster. Add in all the resources to even put it in, and that's a lot of content or other improvements that could be added to the game for the ability to do something we're already getting the ability to do in Heavensward.