I'd have to agree with this. Sakurai builds up teams and disbands them after the games are finished. Who would be left to make DLC when Smash 4 is over?
Since this game is probably going to be more ambitious than Brawl with even more content expanding two different versions of the game, I can see there being left over content that they could not complete. Instead of holding up the release of the game or scrapping the files, I can see Sakurai taking a month or two finishing up that content to release it later as DLC down the line. Sakurai likes to pack his games full of content so idk if he will go the route of on disc DLC for a great amount of content. Besides they can easily make extra money making DLC for many months so I can see them outsourcing the DLC to another in house studio with Sakurai overlooking the content getting in. if it were any other developer this would be close to a sure thing, for Nintendo we still have to question this lol.
I wouldn't be surprised if you could transfer or get stuff special stuff from the 3ds to the Wii u or vice versa
This will probably happen and it will be pretty awesome.