I think you have some interesting suggestions but even if they added something like that my guess is that the overwhelming majority of people will still choose to fly.
Unfortunately the only way they can make ground mounts “useful” is to restrict the use of flying mounts for a while each expansion. And, well, we all know how well that goes over with everyone.
Would be neat. I think Blizzard is taking a little bit more time with dynamic flight (adding it to more mounts in The War Within) before expanding the system to ground or even aquatic mounts. I like the system, and the ability to swap between the options in The War Within is good for people who prefer traditional flight over dynamic.