The idea that the maps would have to be rebuilt from the ground up is simply wrong, no matter how much it’s repeated. At the most a bit of collision data would have to be added because there are actually very few facades in GW2, with the notable exception of Divinity’s Reach and a few other cities and places beyond the edge of the map. Anet already has a system in HOT which kills you if you leave the edges of the map in place to stop map breaking, it just hasn’t been fully implemented yet. If you want to see it for yourself, go to the Asura home instance and try to leave that map. You instantly die. Collision data is also pretty well implemented even in areas not normally accessible as has been found by a large number of map breakers and explorers. The biggest problems would be the main cities, especially Rata Sum, and I could see gliding being restricted there. Also jumping puzzles would need some sort of downdraft condition to prevent gliding, but would be entirely doable.
Since you can never glide higher then your starting position without updrafts (which there wouldn’t be in the core game) there is a pretty hard limit to what you can reach, especially since in the main game most maps don’t change in elevation very much. And again most buildings and other structures you would now be able to land on have collision data even if you aren’t supposed to be able to reach them. I’ve gone to a lot of places you aren’t supposed to reach through creative and patient jumping and I can’t think of a time when I’ve found a place that was just a facade. Some places are not very detailed but that’s no big deal. In fact I was shocked how much was completed of areas you never were supposed to reach. The map that stands out to me is the Eye of the North map. Back when it was easy to break out of there using teleportation you could explore the area around it and the map was remarkably built (with the exception of underneath the structure of the eye which required some work to get to), even including collision data and trees even though you weren’t ever supposed to go there or even really see it.
And honestly I don’t understand why people care about map breaking anyway. If you’re doing it on purpose then you expect to see some things messed up, and when it happens accidentally it’s more funny than anything else. The Skyhammer map has a bug which drops you out into the trippy watery world below on respawn that’s fairly common; it’s happened to me twice and while annoying because I couldn’t participate in the match, it didn’t destroy the game for me.
And while it probably seems like a small thing to some people, for me bringing gliding into the core game would be huge. I doubt it will happen, which is a shame because gliding is my favorite thing this game has added in three years, but to experience it I’m forced to stay in the HOT maps. And I’ll be honest, the HOT maps are starting to wear a bit thin.