Allowing more flying mounts to be used as ground mounts in no-fly areas is definitely something we're looking into. Right now, we sort of place flying mounts into three categories: Those that already make sense running around on the ground, and look good doing it. Those that would require a few more animations before they'd really look and feel appropriate. And those that would still seem out of place no matter what kind of visual tweaks we'd make to their ground run/walk.
Hippogryphs are a good example of a flying mount that we feel could work in no-fly areas with some additional animations. It's something we'd like to do in the future, definitely, but we wouldn't be able to guarantee any sort of timeframe when a change like that could occur.
