You would have to have a competitive signal with 102.9, which La Raza 98.5/103.3 does not.
If one of the Missouri City sticks winds up being flipped to Regional Mexican (presumably after a sale/spinoff) then Univision might have a fight on its hands. But the Univision folks are pretty shrewd in responding programming wise (tip of the hat to David Eduardo) so Estereo Latino would probably win that battle, too.
The one thing that might be the eventual downfall of ES is if their target demos simply become tired of the format, and are ripe to be plucked by something newer and fresher.