I reckon it will be a big success. But, honestly, I believe video-game only hardware should no longer be a thing in 2017. Almost all features of the Nintendo Switch could have been built on the top of iOS or Android. Nintendo should pivot to a software only company.
For a number of games that simply won't do. Sure you can write games to be underpowered graphically and still be fun, but there's no guarantee someone isn't trying to run your game on a $50 smartphone so you really have to shoot low to get that to work. Also you're competing against a lot of 99¢ or free games in the appstore/market. Sure they're really bad games, but side by side (in the store) the consumer isn't going to know the difference and will choose on price.
I don't want to live in a world with only free-to-play match-three "action-puzzle" games.
Also touchscreen as controls is terrible for any real-time game that doesn't have a one-to-one mapping from what you touch to what happens. (aka, most of them, besides turn-based) I have to be conscious of not only what I want to do, but where the controls are to do it, since I can't feel them.
Nintendo can't build an iOS device for obvious reasons. By the time they strip down android and customise it enough for it to be suitable for gaming it would be easier to make NintendoOS anyway.