Cadence and Warriors are not new IPs but spinoffs of 2 other IPs each.

Nintendo cant even give many of their current IPs the time of day, so whats the point of adding to the pile? I don't know what franchises didn't happen because of Splatoon, but I do know that that franchise will now be made way before any other franchise that doesn't already sell millions.

Splatoon and ARMS are great and unique games that really didn't fit with any of Nintendo's current IP.  So why not make them?

If there's an idea that's better than the older ones, then use those ones.  I mean, I love Punch Out! to death, but there's not a ton to do with that franchise, whereas Arms presented something fresh, so let's go with that.

Although Im not a big fan, Ill give you Splatoon. Its a creative and well made franchise. 

But if Arms is the best they got this gen, then yeah, give me a new iteration of an older franchise instead.

Im not opposed to a new big IP of course, but I just don't trust Nintendo to give it what it needs. Rather them just pay third parties to do it for them. Astral Chain was great. More of that please.

But that was already the case, which is why this is a terrible, terrible argument. 

F-Zero, Kid Icarus, Punch-Out!!, Earthbound, StarTropics, Wario Land are the ones you listed. F-Zero hasn't been made since like 2003 and and even then it was a third party title. Punch-Out!! hasn't been made since 2009 and was again developed by a third party. Mother hasn't been touched since forever and the creator doesn't even want to make a new one. StarTropics hasn't been touched in forever and unless they just straight up rebooted the series, the demand would be minimal at best (most people don't even know what it is, or what it represents even). And again Wario Land was developed by a third party developer, almost 12 years ago. To be clear, I'm specifying third party because I'm talking about Nintendo's main teams takling new IP. As I already stated, I think third parties are doing a pretty good job of making a decent amount of new IP, what I'm really interested in is a team as legendary as the Mario team making a completely original project, not whether Good Feel or Next Level make another Punch-Out or Wario Land. I'm fine if they do. Though honestly, is WarioLand, another 2D platformer in an era where Nintendo is housing 4/5 concurrent 2D platformer series, really as important as a new IP that covers new niches? 

Now, ok, maybe you could make an argument that the demand for new games becomes fulfilled by new IP, and this lack of leftover demand would make Nintendo not care enough to go into their back catalog and create new entries in once beloved series. This is a fair argument, and I actually think it's one that's very underrated in regards to, for example, ports and remakes. A lot of titles that Nintendo probably would have had to make for the Switch one way or another (whether it be outsourcing or developing in-house) had porting literally been impossible, are now not needed because Nintendo can just port over older games. A new 2D Donkey Kong really isn't needed, for example, when you have a port which satisfies the market. A brand new 2D Zelda isn't needed when, for example, you have Link's Awakening Remake. However, this is a good argument for games that had a chance to be made. In reality, the demand for all the games you listed has been dried for a long, long, long time, with the exception of Kid Icarus but it's a miracle Uprising was created in the first place. 

It's ironic, because you say that Nintendo can't give their "current" IPs the time of day, when none of those are current. I'm not going to pretend like the Wii is this ancient mystical temple that hasn't been visited in a thousand years but, it's pretty old, and those games really aren't current or relevant right now.

Lastly, I think a lot of the same people who argue that Nintendo should make more new IP, are also the same people who argue Nintendo should hire more staff, and that Nintendo should use their backlog IP more. So I don't even really disagree with your premise. I just take that as an example of why Nintendo should expand, whether it be through more partnerships or internally. 

IF they would give a new IP the same attention as BOTW, Mario Odyssey, Smash Bros and some other big ones, then fair enough. But we both know they wont do that, so whats the point of asking for it? They will give those franchises most of their resources and we`ll get a few smaller games here and there. Even Splatoon was pretty small when it came out. A short campaign and a few maps. It expanded over time because it became a success.

I don't know. I do like some of their smaller stuff like NES Remix on the WiiU and 3DS, but this gen has been awful when it comes to new IPs imo. While their current IPs have gotten really great entries.

Maybe Im being a bit pessimistic, but I really like the way they are doing stuff now. Backing games that would otherwise not be made. Like Bayonetta 2 and 3, Deadly Premonition 2, MUA3 etc.

Splatoon was "small" as a game but it's marketing was massive, this is something that a lot of people overlooked until the game became a big success. I also remember Splatoon getting new content pretty quickly after it's release which, like, isn't a sign that the developers thought the game might not be big, quite the oppsoite. If anything that's a sign that the devs expected the game might be big, and decided to rollout content they had already developed to try and maintain a presence. 

I don't even think we really disagree tbh. It sounds like you're saying you wouldn't mind Nintendo making more third party titles that normally wouldn't be funded, which I'm not against, and I'm happy with what Nintendo is accomplishing with third parties right now as well. I just don't think that really enters into the discussion of, should the Mario team take a crack at a new IP, or should the Mario Kart team try a new IP after Arms. 

Cadence of Hyrule, Mario + Rabbids, and Fire Emblem Warriors aren't new IPs. They are cross-overs. 

One way the Switch is different to me, is that when Nintendo has a really successful console, they usually have a new IP that sells well on the very first attempt.  The Wii had Wii Sports and Wii Fit, but if you go back further Super Mario Bros, The Legend of Zelda, Metroid, and Donkey Kong Country all sold very well when they were brand new IP.

I don't think Nintendo is trying to do that anymore.  I do see them making new IP, but it doesn't seem like they are either willing or able to knock it out of the park on their first attempt.  Instead, what makes the Switch stand out is Nintendo taking existing series and bringing their latest games to a whole new level.  Just look at the Switch games that are commonly said to be "best in the series" (and also selling far beyond what they have done before):

Zelda: BotW
Splatoon 2
Super Smash Bros Ultimate
Fire Emblem 3 Houses
Luigi's Mansion 3
Animal Crossing: New Horizons 

It's kind of amazing when there is a Nintendo system this successful and there isn't a Pokemon game or Mario platformer that stands out far above the other IP.  Instead the Switch just has a lot of really big sellers.  They aren't just relying on a few big IP anymore.  They have a lot of big IP, because they took some of their small to medium IP and seriously upgraded them.  And of course Mario Kart, Pokemon and the Mario platformers are still pulling their weight, but they aren't doing it alone anymore, not by a long shot.

So, I think Nintendo's approach to new IP now is to give it time.  They won't knock it out of the park on their first try, but they are going to try raising the bar with every new entry.  Who knows?  Maybe the next ARMS will sell over 10 million?  Or the next Xenoblade game will be as successful as Final Fantasy 7.  I think that is the approach Nintendo has now.  They are playing the long game.  They are making new IP, while putting a lot of effort into cultivating their existing IP.

A crossover between two old IPs is not a new IP, so Mario + Rabbids, Cadence of Hyrule, and Fire Emblem Warriors are not.

Honestly, Nintendo has yet to create a truly great new IP since Splatoon. Ring Fit Adventure and LABO come the closest but are still not exactly modern classics and are overall merely decent.