((This is an interesting perspective for me to consider. I used to hate anything on rails and I did everything in my power to push for free flying mounts in vg. After free flying mounts became a thing in many games I terribly regreted my prior position. Perhaps you need a flying mount on your ring or in your inventory to access the railed flying mount travel? That could be a fair compromise.))
Much as I loved Vanguard there were a few things that it added after release (perhaps in desperation) that were not necessarily beneficial. Flying mounts were among them. They did let us get easily to many things that had been developed with the intent that they not be easy to get to.
Flying mounts might work well in a game developed from day one with them in mind. Perhaps with mostly dungeon content so that flying over landscape does not bypass a lot. But personally I much prefer an active and vibrant landscape. Despite a strong D&D background that is one reason DDO never appealed to me.