He says they're experimenting with no flight, seeing whether or not they can create a world where there's no flying but people aren't bothered by it. Sounds like they want no flight, but are worried about pissing off players.
Personally, it'd seriously put me out if they took flying away. To me, the "world" in warcraft is a bit of a joke, at least in contrast to how the developers see it. Like this guy being interviewed who uses unbelievable phrases such as "high octane" to describe the next expansion. Give me a fucking break. WoW's not an action game. It's not "edge of your seat". It's not exhilarating. It's not impressive. It's a decent, uneventful game that gets its legs from the longevity of the content, not its "awe" factor. It is not about "the world". It is about grinding the same content over and over and over, all the while trying to keep your from getting too bored of the tedium, aka keeping your sub.
So for me, when I hear devs get so pumped about "bringing back the world" by forcing people to stay on the ground, I get really annoyed because players will be mystified with the world for maybe a few months, tops, then get used to it. At this point, it will start to feel like the wow we know and are comfortable with, not "the new expansion". Sure, you've got things like class redesigns and new talents to keep people excited for a bit, but Jesus Christ, we're not impressionable 12 year olds playing our first adventure game. The world is not alive, despite all this rubbish they advertise every single expansion. It's not Skyrim. It's not dangerous, it never has been. It's not about playing the game because you are just constantly dumbstruck by beautiful vistas and hidden treasure-filled caves and mystery, it's about grinding and repetition. It's about get X rep from X faction by grinding X mobs so you can buy X gear. Oh, you capped it out this week? Enjoy your break. And oh, you're done with X rep now after two months of grinding? Here's Y and Z rep. Now go do the same thing that you did for X. Oh, hey, look, it's Timeless Isle. Want this shiny mount? Go kill thousands of elite mobs and then you can have it. Dat dynamic content! Once again, it's about longevity.
All that to say this: "the world", especially once you hit the level cap (even more so on alts), will inevitably stop being mysterious and start being an obstacle. As far as I'm concerned the world should be practical. It should exist enough to make you feel like you're actually traveling around - like you're actually playing a game - but it shouldn't restrict you by putting armies of mobs between your point A and point B and then call that "immersive" and "interesting". It shouldn't put conquest vendors out in the middle of nowhere just so you can hop on a flight path then afk for 5 minutes while your bird-taxi on rails carts you to your destination, and then claim "hey, it's getting players out into da world, guiz! Immurshunz!" That's bullshit. It also shouldn't artificially inflate the time you need to spend in a zone just because it can (see: Isle of Thunder, aka the zone I like to think of as a monster mine-field. Shit is everywhere.)
Also. Just for funs. Blizzard does get bonus points from me for designing the collector's edition mount as flight-ready Anzu (people always wonder why that stupid bird couldn't fly)...only to have us not be able to use it to fly around on it at launch. That's fucking hilariously ironic. Almost like it was planned as a joke. Great job, Blizz.