I sort of think the dock may just be a handy way to plug into the TV. But I personally hope that it's just a place to put the tablet so it can access all the inputs and outputs without having to plug all the cables in. For example, The Wii U dock isn't really necessary, it's just a handy way to charge the game pad. Same with the original 3DS dock. What if I'm going on a long trip for awhile and I don't really want to pack the dock. I'd love to just take the charging cable and a HDMI and be able to plug my switch into a hotel TV at my destination.
I certainly hope the dock isn't necessary as I think it harms the portability of the Switch.