So I was thinking with the little quality of life Rek'sai buffs that are coming out to maybe throw some ideas out onto the table for thought. Rek'sai only has 2 skins currently available to her and is a somewhat old champion by now. I feel like she deserves a skin to go along with these little buffs after all this time. So here's a few ideas to go along with some current skin series themes:
Praetorian Rek'sai: Utilizes similar particle effects as her Eternum skin, but with the unintelligible "praetorian" sounds the other skins have. A simple skin and cheap skin that adds a little more variety to her selection!
Battlecast Rek'sai: Significant visual changes, altering the sound of her "voice" to sound like the typical intercom-ish battlecast sounds, particle effect changes for examples that might change her Prey Seeker to a missile, her head rotate into a drill for burrowing or some such. And model tweaks that would turn her legs into similar terrain treads like Skarner's to give her more of a machine appearance.
Program Rek'sai: Maybe some sort of half way point between my previous two ideas that would change her voice up in a unique manner to sound like some sort of rogue computer vibe. Some particle effect changes to match the color themes, with a burrow effect somewhat visually similar to (but easily distinguishable from) Program Lissandra's "legs."
My biggest idea for it all though, and perhaps just some pipe dream however...
PROJECT Rek'sai: Complete aesthetic overhaul of the champion, another legendary skin to add to the pool that gives her vastly updated particle effects to fit the PROJECT art style, a model that suggests she once was a burrowing queen of the void but was repurposed into one of Project's experiments to turn her into some form of enforcement. But the main point of this skin.. to give her a voice. An actual voice, with lines of dialog and everything. The idea of a Project implementing some sort of their tech to give Rek'sai the ability to speak with an understandable voice to assist in brainwashing her to do their bidding I feel fits the theme very well, but let's not forget that Rek'sai is the burrowing QUEEN, a beast of the void whose fury rips through sands and helpless victims. Rek'sai would start off the match with quotes that support Project and the fact they "enhanced" her, and "gave her a voice." She would praise them, but leveling her ultimate would give her new lines of dialog to speak. Memories of all the torturous experiments done to her would surface to be clearer each time she reached a level up for her ultimate (which would go along the lines of filling her with unexplainable rage at first, and more obvious why later on.)
These were just some ideas of mine I've been thinking on. I know Rek'sai isn't the most popular of champions and the whole idea of skins is to sell them, but maybe with some buffs to the champion and a new skin it might bring a surge of people to play her again.