I have already pre-ordered WoD, and I am okay with no flying. I'd probably be fine without it through the whole expansion. However, it depends on a lot of things, such as how the zones are designed, flight paths, where quest hubs and raids are in relation to capital cities etc. It sounds like Blizzard are designing Draenor with these things in mind, so I have faith that players won't actually miss flying as much as they think.
To me that's definitely a welcome change, and it's something I enjoyed about the Isle of Thunder. The place felt dangerous because you couldn't just fly away from things, or drop down only where you needed to. I will say though that I missed flying on the Timeless Isle. Some of the mobs on that island are a pain in the ass and not fun to deal with.