At the end of the Mag'har recruitment quest, when you land back in Durotar from the portal, you see several botani, saberon, and I think some magnaron running towards the Barrens.
In this vid @ approx. 24:29 you see black saberon running along the mountains past the elementals. And when the camera pans more to the left, you see botani running past a tree. The saberon could be considered enough to start a breeding population as ingame doesn't accurate reflect lore - they are apex, sentient predators. If they have the correct amount to start a population then they could be an issue. The botani are a far worse issue. They could quite easily use the overgrowth in the barrens to start their own Everbloom.