Consider this:
How many flying creature types are in DDO? Dozens (if not hundreds)
How many flight-based quests are in DDO? Zero.
DDO has evolved and expanded greatly since inception. So many things have been added over the years, but why not flying? Flying creatures or flying mounts would add a great deal of interest in DDO and help add a whole new dimension to gameplay. Some of the best parts of other MMOs have been (in my opinion) flying (or space flight) missions/quests. It has it's own virtues in terms of game development: Experience, upgrades, mission capabilities, player skill, enhancements, etc.
So why hasn't this been developed into the system? DDO's main engine has stayed largely the same for years now, while hardware continues to improve. Any concerns for computational ability are somewhat irrelevant as there is a low-res engine for very old systems, and many other MMOs (newer and older) incorporate flying, thus proving the feasibility. Futhermore, flying machines could easily be justified as artificer creations, domesticated creatures, or simply magically imbued objects (but that sounds a lot like artificer works).
I implore the developers to consider implementing flying into the game! Don't just add more of the same, add more variety as well!
**EDIT**
I do not mean to say we should have the Fly spell (from Reaver's Refuge). I am saying we should add flying machines or mounts. And, these flying machines/mounts are only useable in certain zones, NOT in currently existing content. (Nearly every other MMO with flight has this clear separation)
You could even make a whole new world, in the same way that Eveningstar is a whole new "world." Make it an expansion for all I care. But the point is, new flight mechanism, new worlds, new quests, and a whole new way to look at DDO.
It would add a great deal of satisfaction to the game, in my opinion. It would add a completely new dimension to DDO, and something the game has lacked since day 1. Fighting a dragon in the AIR would be MUCH more interesting than fighting it on the ground.