For reference, I still play That Other Game(tm).
One of the many things I love about Rift is that there are no flying mounts. I would not object to them if they were added, but I really do like that we are all wandering over the land together.
Flying mounts would really change how Rifting works too, putting those who are only on land mounts at a severe disadvantage. It's already hard enough to reach a boss when folks with much faster mounts get there and start blowing him up. He dies and you've only just gotten to him, or are only half-way across the zone. Flying mounts would make that many times worse.
So, I'd prefer to not have flying mounts.