Yeah it would have to be cheap. A $200 "dock" that is basically just its own console is a non-starter.

$129.99-$149.99 with a game bundled in ... maaaaybe.

There are still lots of logistical hurdles here too, I think Nintendo would have to mandate that all games are playable on the regular Switch for people who don't have the dock.

this would a gold move from Nintendo, we could really have it all

Yes it seems this is approach that Nintendo will take and something similar is very posible, but don't expect this in near future, maybe in 2-3 years.

In 2018. for instance we can expect Switch Pocket that will be smaller version of Switch, without dock and controller just for outside home playing. Later we could expect dock that will have more power or just powerfule Switch home box.

A "Switch" device that can't "Switch" kinda betrays the whole name/point of the concept.

I don't see a smaller Switch not be able to do the TV streaming stuff. It's all fairly simple at this point anyway.

Even an HDMI dongle in the future (like Google's Chromecast) could handle wireless streaming to a TV. There's no reason to gimp functionality like that. 

The dock supplies power. That power could run a fan and deliver a significant power boost to the processor making the hardware significantly faster. Tegra x1 and 2 chips have more transistors than xbox ones. A custom one with a high performance mode for when it is supplied adequate cooling and voltage could do quite well; no additional chips needed.

This will highly likely be the case. As far as I know, Nintendo got a patent for that. So, they will use it in the future. It will be a similiar concept to PS4 and PS4Pro. Those who want better visuals, will go for the higher price.

it could be a good idea, but we'll end up with games (mainly third parties) that will be Switch pro only and won't work on the handheld set up. And Nintendo won't exploit the pro properly, since they'll always try and make their games both playable on handheld and TV mode.

So it will be a mess.

Sooooooo.... Nope.

That would be an awesome idea, but I don't think it will happen..

Not if it still functions as a dock for the regular Switch.

Why would it need extra hardware when you can just clock it higher in the dock. That should make a good performance boost of at least 20-30%.