With how many moving parts this thing has and how many different play styles I believe there could be a wiiiide range of accessories for the switch.
Starting off with the Joy-cons there's a multitude of things for this. Skins for the Joy-cons, maybe grips that single joy-cons can fit into while you hold them sideways, maybe different things to slide into the top for something… then not to mention the possibility of third parties making knock-off joy-cons without some of the more expensive features like HD rumble.
We get to the switch itself with again more skins, screen protectors, cases etc… but then the possibility of companies making differently styles Joy-cons means we could hold like half a gamecube controller in each hand. (Idea based on one picture that was floating around someplace.)
There's a lot that companies can do with the Switch here and i'm interested to see where accessory companies might end up heading and we might have a bigger selection of things that end up being cheaper and possibly just as good as Nintendo's quality…I mean i've bought knock-off of things before and they have been working just as good as name-brand stuff.