I'm trying to look at things from Microsoft's perspective.  From what I can tell they brought Cuphead and Ori to the Switch, because they were worried about Google getting into video games and expanding their influence over the internet.  Microsoft technically announced xCloud just before Stadia launched, but it should be obvious by now that xCloud was not ready to the extent that Stadia was.  They were worried a lot about Stadia before it launched, but now it seems like Stadia is a dud.  I wouldn't be surprised if xCloud gets delayed more now that Stadia seems like less of a threat.

So going back to Cuphead and Ori, I think this was a preliminary move.  Release small games on the Switch first.  If Stadia became an unexpected success then Microsoft could start porting their bigger games to Switch too.  Basically Microsoft was prepared to fully back the Switch just to fight Stadia any way they could.  But now that Stadia seems like a dud, I don't expect many more games to be ported to the Switch.  When Cuphead was ported over, Microsoft said that a physical version was coming.  Where is it?  It's been over a year and it's still not here. 

Now that Stadia is doing poorly I don't expect to see much more come from the Microsoft and Nintendo "partnership".  They might occasionally release some small games on the Switch like Minecraft Dungeons, but I don't expect much more than that.  Those little games are basically just insurance.  Stadia had a poor launch, but sometimes a new experimental product starts out poor and then grows slowly over time.  So, Microsoft has this relationship with Nintendo as an insurance policy.  If Stadia ends up growing in success then Microsoft can start supporting Nintendo big time with all of it's larger games just to keep Stadia from growing in market share.  As long as Stadia appears to be a dud, I don't expect Microsoft to port any of their bigger games to the Switch.

I'm not sure what Microsoft gets out of it if they port their big first party IP's like Halo, but Rare Replay should've been a Nintendo/Microsoft joint venture to begin with. That way it could have also had Diddy Kong Racing and Star Fox Adventures, maybe even Donkey Kong Country, and be released across XBox and WiiU, with a Switch port later on.

Firstly Microsoft will be fully converted to PC gaming.

BoTW in an Xbox One alone would be gorgeous... 

Nintendo and Microsoft both benefit if more Nintendo fans become Halo fans.

It takes nothing away from the XBox ... if you love the older Halo games on Switch, you're simply more like to choose an XBox SX or xCloud over a PS5 at some point.

The only loser in this scenario is Sony because you have more of the Switch audience becoming pro-MS.

This is an "out of the box" way of thinking for MS, but it would be smart. You're never going to get Nintendo to agree to giving MS games, so just forget that, that doesn't mean you can't benefit by leveraging the Switch audience to be more friendly to your console over a Sony one. 

They want to make inroads against Sony? They are going to have to start thinking outside of the box.

MS could very easily become the no.1 publisher outside of Nintendo on the Switch and begin to cultivate a real audience that loves their IP and that will pay dividends for them down the line. 

KI maybe as the series history but the rest? Nah they should stick with the Xbox brand of systems/services IMO.

The hardware is the storefront for these guys.
MS want to sell you services and subscriptions, and going 3rd party and porting everything onto other systems, while makeing them more money from game sales, would go against their idea of being a service provider. So thats unlikely to happend, because it doesnt fall inline with how they see themselves going into the future.

You could argue it could be used like a gateway drug...
Give them older games, from like a gen or two ago, so Nintendo users could experiance some of the 1st party games from xbox.
That way if they like them, they might want to give the newer games a try and opt to buy a xbox console.

Actually wouldn't it? 

If I'm a Switch owner and I view MS/Sony as basically the same but I become a big Halo + Killer Instinct fan because those are on the Switch and I enjoy them ... guess which streaming service I'm more likely to choose ... xCloud + Game Pass please. 

Getting lots of fans of MS IP on the 100+ million Switch user base would be great for xCloud.

Would nintendo allow xCloud and Gamepass on Switch, if they know it could cut into their profit margins and game sales?
Maybe they would if Xbox gives them like 30-50% of the profits (from the servies on the switch), which then forced MS to up the price of xcloud+gamepass abit on the switch..

I think its unlikely to happend though.

Series history is one thing, MS needs to sell more consoles period. 

Getting more Halo fans on the Switch helps that. 

If they want to sell more systems they have to start thinking outside of the box, Sony is not just going to gift them marketshare and they're stuck spinning their wheels for 3/4 generations in the same situation (way behind the Playstation).

Try something new. No one is going to say "well I'm not buying an XBox SX now because the Switch is getting a 10+ year old Halo game".