I don’t know any reason why Ogres haven’t been added as a playable Horde race by now. However, the fact they’ve been considered multiple times tells me that Blizzard had some sort of interest in it for the considerations across multiple expansions. Granted, it’s hard to know how Blizzard feels these days about it.
The only big hurdle I really see with playable Ogres is getting the two-head customization working, which would likely be expected with playable Horde Ogres. As mentioned before, the game’s coding is likely a nightmare to delve into, and I can only imagine how much of a headache it would be to get two-head options for male and female Ogres, complete with their own separate customization options and helm transmogs. Seeing how Dracthyr customization has been handled does give me hope that the work needed would be possible and could happen.
However, in a marketing sense, I do think that getting that to work along with female Ogres would be pretty big marketing news. Getting a Horde race that people have been wanting since the game launched with such features would be pretty huge. Sure, there wouldn’t be elf numbers of players making one, but popularity hasn’t really stopped some races from becoming playable.
All we can really do is keep up the support for playable Horde Ogres as we go through expansions. I don’t see it as an impossibility, even if it has been far too long to have any Horde Ogre activity in general. I’m still keeping hope, myself.
Dream big, Ogre fans! 
