They've GOT to get it in for £250 or less. It will be 100% dead in the water if it's going up against PS4 Slim / Xbox One S bundles which are already selling on Amazon for £240 WITH a game bundled in. You can buy a PS4 slim with Call of Duty Infinite Warfare bundled in for £219 on Amazon UK too right now.
If they can get it out for £200 that would be incredible as that would start putting it into impulse buy territory for alot of people.
Nintendo simply doesn;t have the kind of traction with younger people that it used to for them to release an expensive box which is less powerful than its competitors (which it will be). I work in a Primary School and most of the kids there (ages ranging from 4 - 11) play games on mum / dad / older brother / sister's tablet, or they play games on a Playstation or an Xbox. When they talk about Pokemon they are talking about Pokemon GO, not a mainline handheld game. When they talk about games they play / want they're talking about Minecraft, FIFA, Destiny and sometimes Call of Duty. Most of the conversations I have with the kids in my class are about who I've got in my Ultimate Team. The older ones talk about Assassins Creed etc. They're not talking about Splatoon, or Donkey Kong or Mario Kart. This is a shame as these games are way more age appropriate than much of the stuff they are playing but that's a different topic.
My point is, Nintendo can't afford to release a machine which has less impressive graphics and can't play Call of Duty / FIFA (although we don't know if it will be able to do these at launch - maybe it will!) while costing more money. It will kill the unit before it's even got going.
IF they can get good software support then it may well gain ALOT of traction though. If people think they can play a PROPER version of FIFA (not the crummy tablet versions) on the go then that could well make it a very tempting purchase. The Price has GOT to come under £250 imo though. Any more will be a serious problem.