I was actually planning to buy one on day 1 as a mainly handheld console. I never bothered with a 3DS and my Vita is starting to get old but can keep me entertained for at least another year. (I own a wiiu, a second vita, both kinects and a gaming laptop and enjoyed them all; I have no need to defend or hate any company).
As for the prediction I think it'll do around 20M-30M so better than gamecube but nowhere near 3DS. If Sony supported Vita for a couple of years they could have crippled Switch easily.
I think going for a hybrid was a mistake, they should have come up with a 3DS successor that has a tv out accessory at 200$.
Buying as a handheld: it is too expensive, especially with 60$ games.
Buying as a primary home console: too weak, not enough launch games, not enough future games, the joke that is the paid online service (I am pretty sure they'll charge at least 40$/year).
Buying as a secondary home console: too expensive, especially with the accessories.
Switch will die of a thousand paper cuts but at least Nintendo fans will have a bunch pointless arguments. 300$ is cheap (for a home console), switch looks pretty good (for a handheld), library has high quality games (but missing all of the seminal games from the 3rd party publishers), ps4's launch line-up was worse (should have taken advantage of this 3 years ago), it won't get a price cut anyway (even though 3ds got one in a couple of months), online play is (probably) cheaper (the rental games are a joke/insult even if PS+ declined this year) etc.
The main problem is how easy it is to ignore all of Switch library. Yeah I liked the Zelda trailer as well but there are and will be enough great games to last a lifetime without ever playing a Nintendo game again. There isn't a unique experience that is not represented somewhere else. The same is true for the other two, I love sunset overdrive and bloodborne as much as the next fan but I have so many good games waiting for me to try them out on the systems I already own at much cheaper prices.