It's usually a 6 year wait between titles, actually. However, I don't think that'll be the case this time, because I think Nintendo will go for a quick remaster/cheap sequel like MK8D or Splatoon 2 were.

The thing is, these games don't really take that long to develop. I believe I remember reading Smash 4 had a development cycle of about 2 and a half years (plus 1 and a half year post-release, I guess), which means the only reason it didn't release sooner was simply because Sakurai was doing other stuff (Kid Icarus). However, if Nintendo really wanted it, they could have very well began developing a new title in 2016 or so, and it could be ready by holiday 2018, especially if it is a sort of Smash 4.5.

Edit: ...and I don't see them missing out on that possibility. Right now, Smash is the one biggest missing thing on the Switch and Nintendo will want to address that, especially with Smash 4 continuing to grow competitively and still being on a console they want to erase from existence.

Edit 2: wait. This is my 8,000th post? Woo *party*

I think Nintendo has pretty much reached the end of graphics improvements. All of their characters and franchises are cartoon based, so there's just no need for hyper realism. A result of this will be more games that seem like asset flips or cheap sequels from Nintendo. It should also result in faster game development times and fewer droughts. 

Nintendo could announce Smash 4 Deluxe or Smash 5 in January and have it out by summer. They did it with Splatoon 2. 

Congrats on 8000 posts. I still have a long ways to go to hit 1000. 

I don't think they have reached the limit of graphical improvement just yet; games like Mario Odyssey and Splatoon 2 still show some visual improvement over their Wii U predecessors.

Splatoon and 3D World were both budget games though, so they aren't hard to top. One was a new IP and the other one backpedaled the Mario franchise for the sake of cashing in on the four player aspect of NSMB. 

So what, you think from now on games will just stop looking better than their Wii U predecessors? That seems highly unlikely.

No, I think Nintendo won't make games on the level of PS4/XB1. That's what I mean when I say they've stopped developing graphically. 

The Switch hardware itself is less powerful than PS4/Xbone so making games of that visual calibre is impossible in the first place. But they're clearly not stopping at Wii U levels of graphics either.

You get what I'm saying though right? Nintendo isn't going to make games that are graphically on par with PS4/XB1 until almost a decade from now. There's no need for them to do this because their games are all cartoony.