I imagine people were prepared for the passive's potential to be gamebreaking (I'd argue that is actually is gamebreaking, but that would derail your thread slightly, so I'll avoid that subject for now). A number of tweaks are available to resolve the issue if future gameplay indicates that Kallista is indeed overly mobile: Riot could allows slows to detract from either the speed of her dash or the distance of her dash (the latter would work better, as the former could mess up her attack speed), they could adjust the distance she can dash when retreating to promote aggressive use instead of constant kiting, they could adjust the distance for both advancing and retreating, or they could increase the portion of Kallista's attack animation that happens before the projectile launch, which would, without reducing her speed or the frequency of her jumps, keep her in one place incrementally longer, thus opening her up to more skillshots and/or gap closers.
So a number of potential levers exist, and I'm positive that if Kalista proves to be a huge issue because of her mobility then Riot will take one of the steps above (or a similar approach) to remedy the problem while keeping her passive's identity intact.