@Riot, Thought's on Rek'Sai's kit
She's being pushed into obscurity with all these nerfs and is slowly losing her identity, so I believe there's really only one way to truly balance the champion.
Change her Void Rush (R) from global to 2500/3000/3500 range. This change alone would make her early game pressure far less as you could really only utilize the map if you're within range of the tunnels. This would punish her ability to back then just Void Rush (R) back onto the map within seconds.
This change alone would take away so much from her kit, but would still give you the same effect as Nocturne or Twisted Fate with map pressure. Also with this change, it would make Rek'Sai's map pressure less than somebody who does not need to prepare their ultimate before using it.
EDIT: With this nerf, they should revert the knock up radius and HP reduction from 611.2 to 570.