A pretty god idea, actually, although I'd still rather just have an old handheld console and use a flash cart.
It is further evidence of Nintendo seeking to monetise its old back catalogue on new platforms and likely a big reason behind its copyright enforcements against hosts and distributors of even its oldest IPs.
Not with a design like this, as it only covers the oldest two-button games.
Anything that requires ABXY and/or shoulder buttons is immediately excluded without altering the design.
One would expect that Nintendo would have to produce quite a few SKUs to make its product ready for the wide variety of smartphones available nowadays.
For just this SKU, no. I can already see how it would work with numerous different sizes of phone… but if Nintendo are reading this and want to know how, they'll have to offer me money for it!! :p