Rek'Sai and Displacement
Just a thought I had. I'm sure there'd be many barriers for it, but I think it'd be pretty neat if displacing moves (knockups, knockbacks, grabs, etc) forced Rek'Sai out of her burrowed state. It'd be a bit of a nerf, as it then removes her knockup, but it would fit thematically. Again, just a thought.