I like the Elf thrower idea, but I think Heavenfall is right in the amount of work and the fact that we don't know what Stardock has in mind for city sieges and war machines in general long term. Keeping to existing character based units should keep the 3D modeling more resonable.
With that in mind can I suggest:
Drota: Beast Tamer: mid strength fighter that has a special ability that allows it to take over allied "animal" enemy troops (Spiders, Shrill, Drath, Umberdroths)
Drota: Hunt Master: strong fighter that gives a boost to all "allied" units in the army.
Living Stone: Gargoyle: Faster fighting unit (with wings); could use the new "Leap" ability from Murteas Grimore. (this could have unfortunate overlap with "winged golems", maybe differentiate in stats? winged golems gain movement advantage a la angels, gargoyles have "Leap" as special ability?)
Living Stone: Boulder Hurler: Stationary city defense unit with a longer range and more damage than a catapult. Possibly with the ability to stun / knock back enemies.
Living Stone: Gate Crasher: Siege unit a la catapults, but larger with a significant bonus vs walls.
Golem King: Spell Swallower: weak combat golem that absorbs a percentage of all spell damage done to the army, and also has regeneration.
Also, Goblin fanatics are awesome. Just saying.