Yes the Discord leak was 100% true; only Xbox diehard fanboys & fangirls were denying them. I can't see 3P OEMs making next-gen Xbox devices unless Microsoft at least R&D out a specification & blueprint those 3P can leverage, plus providing them Xbox OS alongside a Windows license and the UI frontend to Xbox OS that they can customize as they feel like (within reason).
Keep in mind, IF the next Xbox systems are truly PC gaming machines, the presence of Xbox OS would simply be for BC and library transition of Series X & S owners to hop over. In this scenario, new "Xbox" games would be Windows versions of those games targeting the new Xbox spec as one of the configurations to run the game on. I think OEMs would have the ability to scale certain hardware features up and down (within limits), add non-essential ports & functions and support for external cards & whatnot depending on device form factor.
That approach though, IMO is basically Microsoft fully "giving up" on hardware in the traditional sense. OTOH, if they feel their upcoming lineup can fuel & justify Game Pass growth, and feel that they can leverage Game Pass to monetize access to alternate storefronts like Steam, while facilitating growth in usage for Windows Store via a proprietary device, they'll make their own hardware next gen and take a more hybrid console/PC business model in areas where it makes sense. Ex; you'd still get builds of games for Xbox OS on the Xbox Store and Game Pass, but if a user wants to play it on Steam through their Xbox, they can do that if they have a certain Game Pass subscription that's active.
Another example: Microsoft's Xbox devices could leverage Game Pass as a soft-subsidizer for upfront hardware costs but the difference is made up in locking one SKU to a 1-year or 2-year Game Pass contract with a slightly higher cost than 1-year or 2-year Game Pass on their own. And on said SKU accessing alternate gaming storefronts would be through Game Pass. But they could put out a higher-priced SKU that basically lets the user access those other storefronts like they would on Windows. Meanwhile 3P OEMs would make versions that function like Microsoft's higher-priced SKU in concept (since they don't own Game Pass, so they can't leverage it), but they can find other ways to make their devices worth it (a SEGA-based system could play a lot into nostalgia, for example).
