10 years seems about the average physical equipment replacement time period, with 7 years at the earliest and 15 to 20 years on the high side..
so 10yr for an O/S seems about right..
BUT, no speculation on which OS will be the dominant OS going beyond 2025... There's no guarantee that Linux or another OS won't overtake MS by then..
android went from nothing to a huge BLIP, courtesy of Google.. however Google is no MS and doesn't want to be one-- too many strings attached to QOS..