Hi Peter,
This topic was a discussion on my weekly tech conference call with the East Coast; and EOL dates were discussed. This appears to be right as I've heard both 2020 and 2021 on the Microsoft Insider Hub newsletter E-mails I get regularly as a long-time tester of W10 (3 yrs. next month).
Even though Mainstream support may be gone, which would give you 3-4 years by 2020/2021; driver support will be maintained until 2025 (which as a 10-year lifespan that the Product Manager of W10 (Gabe Abul) mentioned in multiple presentations around the world as well as on streaming video back in July 2015). This should give you about 8 yrs. of total software life or so. The main thing that will change between the mainstream support date (2020/2021) and the EOL date of 2025 will be sort of like what Microsoft did last year with W7 support. They simply changed providing their millions of customers weekly Tuesday push updates and changed that to monthly updates. Next year they may change that to quarterly or bi-annual updates (still in discussion) as W7 EOL date is rapidly approaching in 2019- 2 yrs. After 2019, all support for W7 will be gone, much like XP did back in April 2014 (with a very few exceptions for business customers).
Remember, too, as came up in our conference call discussion; WinXP originally out in 2001, was also supposed to have a EOL of 7-8 yrs. putting EOL dates of 2008-2009 and even earlier out there. However, as you know
it went for 13 yrs. (2001-2014); 5-6 yrs.
BEYOND what Microsoft originally planned on due to the huge numbers of both business and home customers running it long after it's original intended expiration date.
In that case, occasional updates might still be available for home users as far out as 2028!
Those dates are
"milestones", and like any long term project, they can be changed to occur either sooner or later than original planned in order to suit marketplace demands and the needs of Microsoft engineering and programming resources.
Some food for thought. Your new W10 PC may last longer than you thought!
Best,
<<BIGBEARJEDI>>