While a hit with Hardcore gamers, the Switch is also a great system for more casual players as well thanks to its simplicity and pick-up-and-play nature. Several of Nintendo's titles like Nintendo Labo, 1-2 Switch, and Mario Kart 8 DX are all geared towards more casual audiences. But, they also all follow the family friendly aesthetic Nintendo is known for. For that reason, do you feel Nintendo should try it's hand at "mature" casual games. As in, games that are simple and aimed at those who don't play many games, but with themes and content that aren't so child friendly. 

Not necessarily blood and gore, or M rated. But something geared primarily towards the early 20-something casuals Nintendo has primarily marketed the Switch to so far. Stuff like Hotel Dusk or Night in the Woods is where I'm getting at.

You mean the Touch! Generations games: https://en.wikipedia.org/wiki/List_of_Touch!_Generations_titles
Art Academy, Brain Age, Clubhouse Games, Crosswords, Endless Ocean, Wii series...

I would love for a card game like Clubhouse to return and Endless Ocean too.

Somewhat. But I was also thinking along the lines of Hotel Dusk: Room 215. Something that's more casual, but not necessarily for families. 

I think they should make more games aimed at older players first with themes that don't so far over the top that they're inaccessible to kids entirely. But the majority of the Nintendo fanbase moving forward is going to be adults, it's the same shifting in demographics that happened to the comic book industry over time.

If that means Hotel Dusk, fine, but why not an online shooter? Why not an open world Western style RPG? Why not a battle royale style game? If Xenoblade X can sell 1.5-2 mill on the Switch, given that its a Japanese RPG (not exactly the most mainstream genre), IMO a Nintendo shooter in the vein of Perfect Dark or GoldenEye (tone more for adults, but not exactly over the top violent) today would sell 3+ million copies, Nintendo making a game like Overwatch or Fortnite would clean up. 

There is nothing more casual than Solitaire, and it's as mature as it gets.

I always argued for a Nintendo Dating Sim.

It would make them a lot of money.

Endless Ocean in HD could be awesome.

Nintendo coined the casual games genre with Brain Age, a casual game aimed at an adult audience.
They also delved into fitness games that had casual elements like Wii Fit and kickstarted the casual fitness genre.

Hotel Dusk isn’t a casual game, it’s an adventure. A casual game is one designed for shorter play sessions on the least a daily basis with long term retention: minutes a day, every day, for months or years.

Edit...nvm, misread the post.  Ignore this.

Nintendo's bread and butter has always been family friendly core games, so "adult casual" seems like going the opposite way. Which might be good for diversity, I won't rule that out. :)

As long as we're not strip poker.