Definitely makes a lot more sense for Sony than Microsoft. I think Microsoft believed their own PR for far too long ("XB1 sales are outpacing 360 sales launch-aligned."), hence why they've been so slow to prepare for the next generation.
Yeah, I'm curious how Microsoft really feel about where they are right now. 42m+ is not bad by any means, but since they reached much higher with 360, they know they have the potential for more.
And I just wanted to add to my post that maybe a failure for PS5 isn't the best example to give for why they'd want to hold off, but rather something like this.
Sony are expecting 16m this fiscal year I believe?
16m to a 100m+ install base is still going to be a lot better than say 22m to a 30m install base.
The 6m extra units in growth doesn't offset the 70m difference in install base, which should translate to a lot more software sales.
So during these periods of a consoles life, I think what makes the console manufacturers more happy is if good games come out that generate a lot of software sales.
Of course, there's also the ability to sell games on both the old and new system simultaneously, so the subject is a bit more complicated. But I think one important factor here is that both Sony and MS are probably waiting until the technology they want for their next systems is ready. If they rush it by a bit, it can end up costing them in the long run. And that may very well be the biggest motivation for MS to hang in there for another year+.
Xbox One launched with the inferior DDR3 RAM, so I don't think they want to make mistakes like that again.