Honestly the lack of half races in WoW is... weird, it's human(oid) nature to want to fuck someone new and different (source, all of history, and not are we even talking about colonization, but when populations have relocated peacefully and intermingled). It's weird that the Windrunners are the only open family about this, lol.
Regardless, in WoW currently while it might very well be happening on an individual scale, it would take generations to be a viable population with a separate identity that would fit of a new playable race. The only two half races that seem viable at the current timeline are Half Ogres and Half Elves, given when they were introduced. Half Ogres already have their own settlement, and Half Elves have existed for so long that there should be a sizeable population scattered through Azeroth.
It's far more likely we will see more Nightborne/Blood Elf mixing given the similarity of their cultures so it will be far more accepted; even when Trolls and Elves are closer biologically, Trolls and Orcs are more culturally similar and would sooner and more acceptingly intermarry. We cannot obviate the elves overall view of seeing trolls as "lesser" so that would take a lot of time to shift on a cultural level.
But yeah, by this point, we should be seeing more intermarriage of races with similar ideologies.