First, I'll state the obvious reason that something regarding NK in ranked needs to change: winning is virtually impossible. Sure, winrates may not be too bad, but can anyone remember a game where they or someone else won as NK without the final town member(s) deciding to give the NK the win? I haven't, and I'm of the opinion that if a role can't win without taking advantage of its pitiful ineffectiveness, it needs to change.
The first idea I thought of was to just severely buff all NK roles, but that would only be good for ranked and would wreak havoc on the All Any gamemode, where there can be multiple NK-aligned players in any given game. My thought now is to simply remove the NK slot from ranked play and replace it with a NC slot. Obviously in classic, this would essentially be adding a vamp slot (there are no other NC roles in classic) but, to go along with this change, the NC alignment could be populated with new roles that would be properly powerful in order to be truly threatening as a "lone wolf" in ranked (think pestilence- or juggernaut-level disruption).
The overall theory of this suggestion: NK roles are not powerful enough to realistically win solo in a ranked setting, but they should not be buffed, because they work well in other gamemodes. Therefore, a "new" class of roles (NC is not new, but it's been pretty barren for its entire existence) should be introduced that is specifically balanced so that it can be effective even with no allies.