Check the OP.
This has been said a few times before.
This means it's going away in favour of Windows.
		
		
	 
I don't disagree that the device will run full bore windows.  That much is obvious.  But that doesn't mean it couldn't be locked down like Windows S mode, with Xbox OS shell on top for that "curated" experience.  MS still want to prevent piracy, cheating, hacking on/of the device.  
But I'm asking for a source of your claim that MS will change their Xbox game development environment that they have been working on for 7 years, which itself is a journey of 12+ years to reach that point collectively.  
Full Windows has two primary game dev environments since UWP was deprecated.  The Windows SDK for unpackaged traditional PC games and GDK for MSIXVC packaged Xbox games.  That part isn't changing, unless you can provide documentation which MS would need to start updating 18-24 months before the hardware release.  
	
		
	
	
		
		
			I think their plan is:
- Essential: Xbox Cloud with ads (no day one games even in the cloud) *
 
- Premium: Gamepass PC without MS day one games (just a few indies as day one games from time to time, like PSN) + Xbox Cloud with ads (no day games even in the cloud)
 
- Ultimate: the current one, the only one that will have MS day one games + ads free Xbox Cloud
 
* = Those who got monthly games via Gold/Essential would keep them as long as they continue subscribed
Since GP isn't a profit souce, I think their plan is to periodically keep increasing the price and degrading the service, so users slowly leave GP and go back to focus on buying games and MTX, which is where game publishers and platform holders get most of their profits.
		
 
		
	 
So you took out Consoles from the Gamepass tiers even though MS has stated explicitly several times they're doing "first party consoles".  
The Ads were for the free xCloud tier, not a Gamepass tier.  
	
		
	
	
		
		
			I don't think what the 
runtime environment is will be sufficient evidence to convince Tobi that the 
development environment is changing.
Regardless, I don't see the point of keeping GDK alive after this move, unless 
			T 
		 Tobimacoss
 can explain what exactly is the need for it to exist for next gen games going forward. Its existence makes perfect sense until cross gen/Series X is completely phased out, but I would think its days are numbered at the very least.
		
 
		
	 
Full Windows can run everything, it already runs Windows SDK and GDK games, UWP still runs.  The windows NT kernel on consoles runs both XDK (Xbox One games before 2020) and GDK (Series) games.  
Reason why MS won't stop using GDK is simple.  MSIXVC packaging, designed for security.  It prevents most hacking, piracy, cheating, translation layers like Proton.  The packages are signed and notarized to run on Windows only, just like how iOS apps can run on iOS and macOS only.  That is the reason why you can't get native Gamepass on SteamOS.  
Windows SDK unpackaged games require Denuvo to prevent piracy, and require anti cheats to try to stop cheating.  MSIXVC packaged GDK games don't require those things.  
 
	
	
		
		
			Using 
Win32 + GDK is the primary, supported app model to build games for Xbox console, Xbox Game Pass (both Xbox and PC), and Xbox Game Streaming**.
		 
		
	 
	
	
		
		
			Key Feature is that only Win32 + GDK fully supports all Microsoft Gameplay Services (Xbox Live identity, multiplayer, chat, leaderboards, achievements, commerce, etc.), and is required for Xbox Game Pass[1] on both console and PC.
		
		
	 
That's from the GDK GitHub page.  The question at heart isn't whether MS will stop using GDK or use full windows on next hardware.  Yes, they will both use full windows and still use GDK.  
So both windows SDK and GDK (Xbox PC) games are designed to scale to hardware.  Console versions (mainly AAA) are simply GDK games that are optimized to fixed spec hardware utilizing the GDKX.  
The main question for me is whether they will still enforce mandatory optimization to Magnus hardware using the GDKX.  If they don't, then it's simply the GDK Xbox PC games that can scale to all PC hardware.  That would only make sense to do if MS is going full unification of ecosystem.  Forcing EA, Ubisoft, Rockstar to release on Xbox PC store or not release on Xbox at all. Otherwise the Console form factor will still have GDKX optimized versions that become a separate SKU in terms of licensing and binaries.  .