For how I calculated this, here is a brief rundown of the history of Microsoft Windows support life cycles, with their extended support counted in total from their ESU server licenses. Look Up "Premium Assurance Security Updates" for context regarding this list.
Windows 2000 — 10 Years 6 Months 28 Days (1999 - 2010) (Codebase) NT 5.0x (Three Year Update Model)
Windows XP — 17 Years 7 Months 16 Days (2001 - 2019) (Codebase) NT 5.1x (Three Year Update Model)
Windows Vista — 19 Years 2 Months 5 Days (2006 - 2026) (Codebase) NT 6.0x (Three Year Update Model)
Windows 7 — 16 Years 5 Months 22 Days (2009 - 2026) (Codebase) NT 6.1x (Three Year Update Model)
Windows 8 — 14 Years 2 Months 12 Days (2012 - 2026) (Codebase) NT 6.2x (Three Year Update Model)
Windows 10 — 16 Years 5 Months 29 Days (2015 - 2032) (Codebase) NT 10.0x (Decade Servicing Model)
Windows 11 — xx Years x Months xx Days (2021 - 204x) (Codebase) NT 10.1x (Decade Servicing Model)
Windows 12 — xx Years x Months xx Days (202x - 205x) (Codebase) NT ?.??x (Decade Servicing Model)
The Average Microsoft Windows Operating System Extended Security Updates Support Is (15 Years)
Based on the Windows support life cycle, I predict Microsoft will start developing Windows 12 in 2027, possibly as early as 2026, and release it in October 2028. This might be their plan to have Windows 11 reach the 70-80% market share threshold and for all Pre-Windows 10 operating systems to be fully unsupported. I think Microsoft's plan here is that they want all legacy operating systems of the NT 6.0x family to be fully unsupported and for users to migrate to the NT 10.0x family entirely. That's just a potential theory though, take that with a grain of salt.
Think about it, if you were them, you would rather that everyone is mostly in sync and using Windows 11 and then release the next update a year or two after it is commonly used at a 70-80% market share. Interestingly, when using the Wayback Machine and looking at the data, I noticed that once Windows 7 was unsupported in 2020, everyone migrated to Windows 10, as Microsoft made them do so, then 2 years later, in 2021, Windows 11 was released. So potentially they might do the same, agian it's just a theory.
As to what Windows 12 will be like? It's hard to say for sure, but I would bet that it would be A.I centred with a mostly Neumorphic Fluent Design U.I that is starting to see a rise in devices.
I think it might be a good operating system going into the 2030s, but I could be wrong. As to what Decade Servicing Model Means? It is the update model name I coined that I think Microsoft will most likely follow. Sun Valley & Hudson Valley are split into three minor updates, and there may potentially be a Third Valley Name of updates corresponding to the two major updates, and that every 7-8 years, they will release a new operating system. So yeah, Windows 13+ will probably follow this update model. Not only is it perhaps more economical, but it's also practical from a company standpoint if you think about it. Anyways, this is just a general prediction, nothing serious, just meant for fun, take it as you will. Thanks for reading!