I've been thinking about this one for a while. The character of Velen is a useful one for World of Warcraft as a whole as well as being one of my favorites in the game -- he stands for a rationally enlighten position which seeks to unite the Horde and Alliance in order to hold off the greater threat of the Burning Legion. In that regard, he's WoW's Medivh from Warcraft III. His visions of the future and powerful understanding of the Holy Light give him an unassailable moral authority - it's difficult for any allied faction leader to stand directly against Velen's position, when he makes it known. Luckily for the narrative, Velen is often distracted with seeking visions of the war with the Legion and how to defeat them and he can't always stand against the Horde/Alliance conflict... either that, or he foresees that it will play out in a way that's beneficial to his goals.
But it is this very role as unassailable moral compass that makes Velen a problem in terms of integrating the draenei into World of Warcraft and its storyline.
I'll explain using some examples. The current Battlefield Barrens weekly quest, for instance, is just the latest sign of Horde/Alliance conflict on Kalimdor. The Horde have expanded into Ashenvale, taken over Azshara, bombed Stonetalon, even made inroads into Darkshore (seemingly, at least) by allying with the local trolls. The night elves are reeling from these attacks. Their new worgen allies are stepping up to aid the Sentinels, going so far as to seek training under Shandris Feathermoon. Yet the draenei, who live on a set of islands just off the coast of Kalimdor, have done nothing.
Now, partially this was explained in Velen's leader story Prophet's Lesson, and it was a perfectly valid reason - they were working to repair the Exodar. But in the aftermath of that story, with the draenei having chosen to stay on Azeroth, we have the same problem the story itself explicated. The draenei are on Azeroth, but they're not of Azeroth and for the most part they're not involved with Azeroth, a problem that's dogged them since the end of Burning Crusade. In BC, the exploration of Outland (the former Draenor) and encounters with broken and lost one's meant that the draenei were inherently invested in the story. Tempest Keep was a former Naaru vessel crewed by draenei, the Black Temple was the Temple of Karabor, the center of draenei worship. Since then, however, the draenei have been bit players in the story, and worse, they've felt completely divorced from it. While other racial leaders wielded politics and prepared their people for coming conflicts, the draenei simply stood on the sidelines. When their allies were pushed to the breaking point, the draenei stood on the sidelines.
Even more interesting, the presence of Velen prevents themes of this escalating war from being explored. Velen himself is a much harder, more merciless person than is initially apparent - new draenei players are told by the Prophet to wipe out blood elf inflitrators who followed the Exodar to Azuremyst and Bloodmyst, for instance - but his goal of standing united in the face of the Burning Legion prevents the very real and very interesting idea of draenei vengeance from being explored. The draenei have much to seek vengeance for - their people were murdered, slaughtered, by the orcs. Saying that the orcs were under demonic influence doesn't change the fact that, with no violence or provocation offered by the draenei, the orcs attacked them before they drank the demon blood, murdered them from their elders down to their young children, and inflicted horrors on them in the waging of this one-sided genocide. Under Velen's leadership, the draenei failed to unleash their full mystical might against the orcs, not wishing to engage in a similar bloodbath, and it cost them. Even the blood elves who fought and died against the Scourge can't match the draenei losses, and in all this time, the Horde has never once so much as apologized for what they did.
There's a huge potential there, but Velen's presence prevents it from being explored. At least a few of the old hard-line Vindicators must seethe inside at how Velen handled that war, at how many of their people died. Yet so long as Velen exists as the unchallenged moral authority and leader of their people, any such characters can only do as Vindicator Maraad did and defer to his wishes. Note: I'm not even implying or inferring that Velen is wrong in his longer view. I just believe that it would be impossible for all draenei to embrace his longer view. Some of them would have to reject it, to rebel against his willingness to forgive in the name of a greater good.
This is the essential problem of Velen, as much as I love the old coot (at well over 25,000 years old he may well predate even the dragon aspects) he prevents the draenei from being fully involved in the very war that has made the Warcraft setting - draenei following Velen's example can defend the Alliance, but they aren't going to step up and lead punitive raids on the Horde. Draenei aren't going to cry out for vengeance against Orgrimmar or Hellscream, even though their potential reason for doing so is far, far more than even Jaina Proudmoore could ever muster. Imagine a draenei commander saying to Vereesa Windrunner "Yes, they killed your husband. I grieve for your loss - they killed my husband, and my parents, and my children, and my children's children. And everyone I knew. I was from Telmor, you see, they killed everyone they could find." And the worst part of that would be, it was Thrall's beloved father Durotan who led the Horde in the slaughter of Telmor, and he used information Velen had trusted him with to do so. And Durotan never drank the demon blood, yet his hands were soaked with the blood of countless thousands of draenei who had not only never harmed him, but who had actively helped him as a child, saved him from ogres, even made him and Orgrim Doomhammer honored guests.
And those two revered figures of the Horde repaid the draenei for their generosity by betraying and slaughtering them.
The draenei people have every reason to hate the Horde and especially the orcs -- every reason to want to seek revenge. As inspiring as Velen's charity and willingness to look past that, not all draenei can possibly share his ability to see the bigger picture and a few dissenting voices would go a long way towards making draenei more involved with and invested in the storyline. Imagine a draenei wizard, heir to one of the oldest and most powerful magical traditions in the universe (a tradition so impressive that Sargeras took note of it) who decided to teach her magical skill to the Alliance knowing, even hoping that they would turn her lessons on the Horde? A draenei Vindicator who finally has enough, moves to Stormwind and begins working on plans to help destroy Horde forces wherever they can be engaged? Even a draenei who goes rogue and begins assassinating orcs of note, leaving their dead bodies with notes saying "Vengeance for Telmor" or "This is for Karabor"?
But you don't need just some vengeance crazed draenei -- rational draenei who don't particularly want another war with the orcs (after all, they didn't do all that well the last time) could still oppose Velen and his goals. The Exodar's repair and current dimensional travel worthiness means that at least a few draenei could simply long to leave the world of Azeroth behind. After all, they traveled the dimensions for over twenty thousand years. There's a lot to see out in the Nether, both sublime and terrible - if the draenei aren't going to punish their old enemies, why are they even staying on Azeroth? Yes, Velen said they were needed, but they're not doing anything. A faction of draenei who just want to go see what's out there could be a fascinating change of pace.
In the end, while I don't want to see Velen leave or die or anything like that, I do think that six years after they crash landed on Azeroth, some changes to their society and signs of dissent are not only necessary, they would be useful. They'd add new elements to the World of Warcraft story, give you characters with entirely new motivations, and make the draenei a part of Azeroth, rather than outsiders watching it develop.