I feel 2028 is like the minimum this generation should last. I think 2029 or 2030 would be good for 10 gen machines.
I can't imagine next generation consoles launching before 2028. The tech in the PS5 and Xbox Series X is more future proof than the PS4 and Xbox One were at launch. The industry would also be able to get their pipelines on track after COVID delayed/disrupted game development.