The sole fact that both Horde and Alliance possess all classes shows they have some level of tolerance towards them. That or they are stupid, blind, racists or hypocrites.
After the kind of twisting they did to create Sunwalkers, there's nothing impossible here. For example, Blood Elf druids? Schoolar types that learned the ways of the nature to achieve a better environmental quality in their cities and zones. A botanist of some sort. Blizzard just have to write it.
Personally, the reason why I'm opposed to it is one of the biggest criticisms that I have with wow: inevitable mmo homogenization. Back in the day (BC, vanilla, Warcraft 3, etc...), the races each had their own strengths and weaknesses. Each brought different skills to their respective factions which gave them each a unique flavor in terms of their capabilities.
Nowadays, the races are starting to converge into a singular entity with the only difference between them being how they appear superficially. This sacrifice is likely being made in order to allow more customization in terms of player avatars. This, in my opinion, essentially ruins the uniqueness and feel that each of the races once had and detracts from the overall universe.
Which is why Vanilla was so garbage. It was incredibly unbalanced, classes and specs didn't have clear roles, talents were a mess that could result in a total failure or absolute OP. It is a good thing that races don't affect output that much. People would just jump on the best race for whatever they want, instead of choosing the race for the race itself.
Also, people use 'homogenization' a lot when they don't want something to happen, when in fact, it's pretty relative. We can say classes are already homogenized since the beginning because all of them "have a DPS spec", "have AoE" or "have some sort of CC". Races themselves will cause a lot more trouble with their racials.
"But they can't with the hooves! You'll hear them coming!" You're confusing that with a shoed hoof (like you would hear on horses on asphalt streets). Draenei are not shoed, they have inner pads that provide traction and cloven hooves that can be spread apart as needed (think mountain goat). This makes them have a good grip in all manners of environment, and relatively silent when they walk.
Funny thing is that doesn't require any lore development to justify that. For some crazy reason, Blizz thinks it makes sense for Draenei and Tauren not use shoes/boots. Of course they wouldn't use the same kind
of boots, but the idea that they would prefer or even believe
their hooves are better prepared to deal with whatever threat that might appear than a, for example, boot made of Elementium is pretty much nonsense. They're Tauren and Draenei, not cows. They got hands and they would use some pieces of cloth under their hooves if it made them 'more stealthy'.
By the way, this whole "can hear them coming" is quite relative. Pandaren are incredibly fat but can somehow fight like some sort of Bruce Lee. Tauren and Draenei can be Monks, even though they have hooves, which would be quite problematic to land after doing some hyper-ultra-awesome-kick. And still, it makes more sense than Rogues?
Hooves are a pretty bad argument against them. Specially because there are Grimtotem Rogues out there.
Also, Rogues aren't only about stealth, Rogues are about exploiting opportunities and weaknesses. Ambushing is one of them. Combat spec is different, it's totally about direct combat.