There's a device for that too. It's called The Switch. 

I would imagine the dynamic between the console and handheld switch may be similar to the dynamic between iPad and iPhone: both basically have the same hardware, but with different markets in mind. Portable is smaller, features a dual screen clamshell design, NX can run 3DS and DS applications. It's probably being delayed because they want to release something that is smaller, more power efficient, but isn't too much less powerful.

Hmm, i didnt cont on nintendo selling joy-cons separatelly, neither custom for each game.

About Just dance, i think the home switch would not need a TV. You can just take the joy cons off and play anywhere you are, so is a new way to sell just dance.

Well, I think in 3DS audience, a handheld one, where you can carry in the pocket...

Not for what nintendo is suggesting. They keep saying it is a home console.

But anyway, it would still be a switch.

Well, about the price. I think switch is releasing at sub 300$ now. And the handheld one can be released at sub 200$.
Ok, maybe i forgot to count that home switch would be cheaper too when the handheld launches.
Editing.

Oh, sorry.

Now I got the reference. lol

Why would Nintendo bother making a version of the Switch that can't even do what its namesake says?

The 3DS / 2DS will still continue being manufactured in some form and will still cater to primarily the younger generation of gamers. Nintendo isn't going to release a gimped version of the Switch as an alternative to the 3DS.

And the fact that new Pokemon games are still coming to the 3DS means nothing... what, so because a new console was announced that means Nintendo has to immediately drop software support for all existing hardware, including the 3DS and its 50+ million WW install base?? I don't expect Pokemon on the Switch to come out until at least Q4 2017 anyway, so Pokemon coming to the 3DS this holiday is irrelevant to the franchise's future on the Switch.

Athough I don't agree with all of the OP's description of the device would be, a dedicated portable switch makes perfect sense. Especially in context of all of the things Nintendo has previous done like the Wii with no Wifi, 2DS etc.

-Joycons may only be used wirelessly because controls will be build into the dedicated handheld, indended for peope who want just that, a cheap 3DS style device that they can easily be pocketed and played. But we don't know the nature of the joycon ports to say they wouldn't be compatible with a smaller device.

-Games which are bundled with their own (optional) custom joycon will again not be centred around the dedicated portable. This isn't a problem, simply something that will be blindingly obvious to anyone who opts to get the dedicated portable.

-No switch games will need a TV to play, that defeats the purpose of the hybrid. Also just dance is playable with phones as a control option if it comes to it.  

-compatibility with the dock will always be there imo, it just won't be sold with the device and I wouldn't expect this device til 2018.

I think Nintendo will have both a Switch XL and a smaller one. The 3DS style version would of course be the budget device, so you start removing things like the joycons, the dock, start using cheaper materials, cheaper, smaller screen and you've got a $50 different in pricetag later in the systems life. Theres no meaningful logistical issue at hand.

Interesting concept, but I don' think they will be adding bc for future systems..

Well, I proposed other way of swtich, specific for the device. Switching from a dedicated(with no touch) gaming experience (like home switch used on the go) for a mobile one, and also the option to switching for vertical screen for BC with 3DS.

They will make 3DS forever? In that prediction 3DS woul continue and be the main handheld console until 2018, and would still be manufactured after thatn. In the end of 2018 they would release the handheld switch, that might work with 3DS games too.

And common, I stated that pokemon would came to switch by 2019.