Rek'Sai passive change idea.
Okay so we all know that Rek'Sai's healing is just an utter joke.
My suggestion is replacing or adding to it with an AOE damage passive centered on Rek'Sai when in Tunnel form.
In specific one that fits her theme as, not only the Void Burrower, but as, well, Queen of the Xer'Sai.
Basically when Rek'Sai tunnels, the Xer'Sai will feel and respond to her anger(fury), and begin swarming around her. They will deal tick based damage to her based on her current. The more fury she has the quicker the ticks occur. They could do bonus damage to small jungle monsters.
To make it more interactive maybe make them act as pets, she could move them by ctrl clicking to scout around granting her additional sonar length centered on them.
And her Q's particles could be updated so instead of just a pulse, she sends out a Xer'Sai to attack, which would just make way more sense.
I just feel like having something that incorporates the Xer'Sai in her kit would fit her thematic way better, as a large predatory creature that acts as the head Xer'Sai.