I would be very skeptical of Kai'Sa getting gutted.

She is the posterboy marksman. Look at her kit - it has literally everything a marksman would ever need. On top of that she has multiple good, unique build paths. She doesn't do any one thing insanely well but everything she has is very powerful. She isn't a caster, either - she works with primarily autoattacks in classic marksman fashion. Xayah on the other hand has actual CC and an amazing disengage tool with her ult - if anything she is potentially more volatile than Kai'Sa albeit not necessarily stronger at the moment.

Ashe is comparable to Kai'Sa, except that insetad of being able to skirmish well she assists her team from afar while still retaining some marksman dps, and it's consistent dps to boot. Ashe's ult and Hawkshot are invaluable tools and her slows can keep enemy teams very honest.

Why these select marksmen work so well this season is simple: they function in a world of getting 100-0'd by any two champions that reach them (potentially just one assassin if Flash+Heal are down or matched with Flash+Ignite). What other marksmen need is the ability to emulate the currently successful ones in that regard. Some could use a faster or longer dash - even if it's per ability level - others a larger health pool or some semblence of base armor. Some just need higher base MS than 325 in order to function in these fast-paced games which is roughly the cardio of a sloth (unless they truly deserve it).

What marksmen need isn't for Kai'Sa to be brought into line - it's for other marksman to meet the "Kai'Sa bar" just like the "Renekton Bar" of old. If it means these othewise borderline unviable marksmen deserve less scaling AS, AD or key ability damage to compensate for their newfound playability then so be it - otherwise most of them will begin to rot and see zero play. A single marksman's dps bar Vanye West has never wowed anyone in the first place; the role is supposed to be all about objectives and teamwork. Bring the role back to its roots.