Hmm... From a lore perspective, nothing prevents the horde from being nomadic, or the Ogres from being with the horde. In fact, both things have many things pointing towards them;
Orcs: They wasn't nomadic in Draenor, but all of them were either trapped or renegade some time after the second war, and they're in a new world now, so traveling around would make perfect sense.
Trolls: (Darkspear trolls to be exact) These guys lived on an island before, and now they're in the barren wastelands of the... Barrens... Would make sense to travel around to try to find good spots.
Tauren: Need I to say anything? They've been nomadic for as long as anyone know.
Ogres: Now things get interesting... They were forced by the Orcs to fight during the first and second war, (Though they probably enjoyed smashing heads) and now they're cut off from their homeland, and their very social structure fits very well with being nomades; The strongest leads, and everyone who wish to lead proves himself by smashing the leader... Not the race which builds great towns, right?
Anyways, I've got a few suggestions for the tech-trees

Kodo-tower:
Well... Kinda like the Mammoth thingies of Lord of the Rings during the siege of Minas Tirith... I've just always liked the thought of Kodos wandering around with towers on their backs

And I'm tired of Demolishers, they've been used up

I can imagine that this would be a T2/T2.5 siege unit.
Loa Priestess:
I can imagine that this would be a "combined" Druid of the Claw and Druid of the Talon, being able to heal, and transform into various forms.
I'd say this would be a T1.5/T2 unit, serving as a support unit in its basic form, but then its transforms could be higher in the tiers.
Darkspear Raptor:
Raptors! These must be in the game, cause they're just awesome

I also like the idea of having some animal unit in-game, and the Horde seems like the oblivious choice for that, with their shamans.
Raptors, imagine their role? No, it's not long-ranged support, but it's a good guess! They're hit'n'run units

And I'd say they should have some kind of "pack" passive, which increases their attack speed by 2% per raptor nearby, to a maximum of 20%, just cause that'd be awesome, and they're well... Living in packs.
And also some for humans

Steamwarriors:
Kinda like Thors, these are heavy assault pieces of gnomish engineering, which exceeds in taking a lot of punishment, while being more than capable of dishing some out themselves.
And this'd probably be T2.5, as far as I could imagine
Walls and gates!
Do I need to say anything? A thing I enjoy while being Terran is the opportunity to wall off, giving that "gate", I like having in games.