Balance aside, is there a problem with adding something to Reksai's Burrow Q?
Right now she's pretty awesome, yes, but that's mostly because her numbers are too high and people don't know how to deal with her yet. Against competent enemies, she gets kited forever and she has a lot of trouble engaging. She doesn't have anything interesting to do in fights - most of the skill comes from strategic (mapwide) movement, and once she hits teamfights all of her decision-making pretty much amounts to "when do I knockup" and "where do I stand to hit faces."
The lack of skill expression mid-fight makes playing Rek'Sai into a bit of a numbers game. Either she does well and single-handedly wins games, or she gets shut down and can't recover no matter how well she plays. When she gets nerfed, she'll be useless.
One easy place I can see to add skill-expression is on her burrow Q, though - it's a long-range skillshot nuke that reveals targets. So what? It doesn't help you ambush people - once you've hit (and revealed) them, they know they're in danger. You can use it to poke, but that's pretty at-odds with everything else she's meant to do. What's the benefit of hitting a fleeing target? There isn't one. In fact, the cast time makes it HARDER to catch a target, because that's 0.5s in which you aren't moving toward them with your enhanced movespeed.
So right now it's a strong ranged poke on an engage/ambush champion. It feels like it should have something useful, some tangible reward for landing it. "Target reveal" doesn't count. Half the abilities in the game (hyperbole, shut up) have that already.
Ideas?
Give Rek'Sai massively increased movespeed toward targets hit by Prey Seeker. This will make her less kiteable, it will provide her with a REALLY nice reward for opening a gank with the ability, and it makes thematic sense. Hell, the ability's called Prey Seeker. When she finds prey, doesn't she want to charge toward it?
It also gives her a bit more skill expression in fights. Landing a long-range skillshot for bonus mobility is a great way to reward mechanical talent, especially because the W-Q-move-W ends in a knockup.
's kit more loaded than Lee Sin's. She doesn't need any more features.