They are delaying regular mount flying for dragonriding, as well as zones being developed with "highly vertical" layouts to make ground mount travel as painful as possible to force dragonriding.
Do a regular zone and add dragonriding like zandalari dino glide and we're set.
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It's more than that though, if you're halfway up whatever WA driven glide/dive/hop thingy and your kid needs something, wife calls you in the other room or whatever... you have to either have them wait or bail, probably fall to your death somewhere, and when you get back remember what you're doing and get back to where you're supposed to be.
Otherwise, you want to go to the bathroom and get a snack you have to log off. Maybe you don't feel like logging back on by the time you get back. Very dangerous from a game design perspective.
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All those things can and do also happen during any other activity, such as while doing a quest or whatever else you do in the open world. Was it such a problem until now? Why is it problematic only if it happens while traveling? And those activities are going to be the majority of the time you spend in the world, with traveling from point A to B comparatively small due to how fast dragon riding is.
As a side note you don't fall to your death with dragon riding. You can quickly point the dragon right up so it will stall and very gently drop down while you're afk, or alternatively leave it going and overshoot your destination and possibly land in an awkward place, like you would with a flying mount.