I agreed fully with everything you had to say in your post but I wanted to highlight this - I don't know if it's Sakurai himself who needs to be highlighted as such, but rather Japanese developers and their ideas of multiplayer.
Maybe it's that we're trying to Americanize Japanese developers, which I believe are being left in the dust on this front. Has a single one of them figured this out? Other than the obvious games that will facilitate many players no matter what (Think Mario Kart or Bomberman) has there even been a game or a mode that a Japanese focused studio has really rolled out in the online space?
I can't think of one.
It's true that someone other than Sakurai could have ultimately made the decision. After all, he seemed very enthusiastic about presenting online functionality in Brawl, if I remember correctly.
But Japanese developers in general have embraced online play for a long time. Look at the Dreamcast's initiative with games like Phantasy Star online and Chu Chu Rocket, both of which were developed in Japan. The Final Fantasy series has gone online multiple times. The PS2 had online capabilities before the original Xbox Live was even released.
I really think it's just a Nintendo thing. I recall reading an interview with Mr. Miyamoto about NSMBWii not including online, and he flat out said that that was a design choice, and pointed to their play-testers who had such a good time playing together in the same room. He may even have a point-- I enjoyed Halo 2 with my friends down in the basement with system-link Capture the Flag going on, but I gave up on Halo 3 because those same friends became intolerable online. But even so, I'm not sure how a company can compete in this new industry without basic online functionality in all the parts that are expected.
Smash Run sounded like a fun mode to whip out and play while mobile. It's tailored to a mobile device. It's perfect for that.
However, in order to enjoy it (because playing against the CPU would get old really fast), I apparently need to be with other people in the same room. At that point... why not just play on Wii U instead? It's like, unless you have three friends who also love the mode, each own a 3DS and all live nearby, the mode gets its legs cut out from underneath it. I don't understand the benefit.
Online functionality has its drawbacks, like what the game becomes once servers are shut down, or how a game feels barren if nobody's playing it, or trash talking, or other players ruining your game... etc. But it also has so many benefits when a game seems so
perfect for it. The only reason I purchased Destiny on Tuesday was because four of my online friends from various parts of the country and my little brother (I don't live with him anymore)
all got it and
all want to play with me. If it weren't for that appeal, I'd never have considered purchasing it. Likewise, when I tried to get my brother to buy SMB3DW, this was the conversation:
"Can I play online with you?"
"No."
"Then... why should I get it?"
Word for word.