I think if we take the tweets at face value 2026 makes the most sense. RDNA 5 might be available by then, offering a massive uplift in performance and visual quality. Dedicated AI and ray acceleration hardware, AI supersampling, AI supported frame gen, path tracing, all of it might be on the table.
And MS can always do a mid gen refresh to compete with the PS6 hardware.
Here's the thing. The PS6 will have cross-gen games atleast for a couple of years after release. So we're unlikely to get proper next gen releases until 2030. Which should allow a 2026 Xbox to compete just fine, and by 2030 they could release a mid-gen refresh that can handle games that push the hardware.
Xbox could treat 2027 and 2028 as their cross-gen years, where devs release games on both the new machine and the XSX, XSS. After that they could transition fully to the new one.
And I think devs will be okay with supporting the 2026 Xbox and the mid gen refresh over the course of the next generation. Shouldn't be much different to supporting the XSS and the XSX. Sure, there have been issues with the XSS, but they're mostly related to cut-down memory, which shouldn't be a problem in future hardware.
An early gen might piss off existing Xbox consumers though. But I think it might be a reaction to the PS5's mid-gen refresh. Xbox can't compete with the timing of that hardware since they didn't plan for a mid-gen refresh. Not releasing anything will probably see them butchered in sales. And releasing a mid-gen refresh two years after your competitor makes no sense. So this might be the only option they had.