Nintendo have revealed three distinct “playstyles” for the Switch in their January 13 presentation and announced that up to 8 of them can connect together for multiplayer.
The three playstyles are: TV mode, where the Switch is docked and games are played using either the Pro controller or the Joy-cons in a grip, Tabletop mode, where the Switch uses its stand to rest on a table while one or two people play using the Joy-cons and handheld mode, where the Switch is played with the Joy-cons attached.
Thanks, @Wario64.