In my opinion DDO is one of the most unique MMOs out there, I've played every MMO from UO to AoC back to WoW and everything in-between and played them all at the very end game. After seeing all of these games i have to say the levelling experience in DDO is one of the most interesting and pleasant times i've had, the game has a number of interesting and innovative concepts you just don't see in other MMOs. All that being said the one thing it dose not have is a compelling end game.
The raids that are available are quite easy and there is not much of a reason to do epic 6 mans exhaustively. I do understand the desire to keep content easy enough so that it's accessible to most pugs and so i wont get involved in the "make everything harder debate". But i will say that in my opinion the end game could be made interesting by simply making it more worth wild for players to keep grinding away at epics. Maybe putting in some form of very high end epic item vendor that would allow you to spend large numbers of epic tokens to get very powerful items would be a good start, it may help to make tokens character bound if you were going to implement something like this as well. The vendor could offer these epic items (or artefacts) at a cost of hundreds of tokens. this way players would feel more driven to do more epics and not avoid the more challenging ones.
This would give players more to do at the end game other than TR or sit around waiting for raid lockouts (assuming they still even need anything).
Also don't be afraid to stray further away from the D&D type itemization I played PnP D&D for more than a decade but even the hardest core D&D purist has to agree that PnP concepts can not always transfer over well to this sort of online environment.
Just my 2 cents, thanks for your time.