Coming from the Hollow Knight dev blog...
Quick Update: Switch version is now feature complete! Prep your Joycons (Or your Pro Controller, if you prefer). From now till Hollow Knight’s (unspecified) Switch launch day it’s all about testing and optimisation, all the time. That’s still a task mind you! But things are really rolling now!
And though it may go without saying, Hidden Dreams will of course be included with the Switch version at launch!