Just a little thought-experiment here, something I'm contemplating for my own version of the Dragon Empire after reading some online discussion of half-orc origins:
13th Age gets away from the problematic origins of the traditional D&D half-orc by explaining the species not as the product of sexual violence but as a High Druid-initiated immune response to the return of the Orc Lord and the concomitant rise in orc populations. Walking, talking lymphocytes, if you all.
As a way of avoiding the inscription of rape into the game setting, this certainly works. But it does raise a new question: why use a breeding-related term for the resulting species of pseudo-orcs? Obviously the answer is "because 13th Age tries to preserve the sacred cows of D&D tradition whenever possible," but that meta-explanation doesn't make much sense within the fictional context of the Empire.
What I'm thinking then (and I suspect a Google search would demonstrate that I'm in no way original here) is to recast the half-orcs as an entirely different species: beast folk. The precise appearance of the beast folk is still up for grabs: they could just look like brutish humans with excessive body hair and pronounced canines, or they could have many more animal features, features that might be tied to specific subpopulations (a wolf group, a deer group, etc.).
But the advantage of either approach is that the existing half-orc stat block (bonuses to either STR or DEX and the Lethal racial power) can apply to the beast folk concept without any changes needed. The beast folk backstory also nicely maps onto the existing half-orc one: the beast folk of the frozen north have frequently been enemies of the Empire, but with the resurgence of both the Orc Lord and the High Druid, the Emperor has seen fit to make peace with his former foes and to support them against the hordes on their borders. (Especially since the Dwarf King's attention to the orcs frequently wavers based on whatever is bubbling up beneath his delvings that week.)