It's absolutely true that the console market has mostly stagnated when only looking at userbase. That's extremely easy to prove since we know what every system has sold, and nintendo had to fold their huge handheld base into their console one to sorta mask how bad things were getting for them on the console front (even when adding wii u/3ds together that's still roughly 90-100m units although 3ds is carrying most of that). But everyone is also making more money than ever too and I don't think there's really an impending problem here. Even if the market isn't being replaced with a lot of younger people more and more people are continuing to game into their 40s and beyond, so worst case scenario there won't be an issue for a few decades as we start dying off. If there is a problem here it's microsoft becoming so irrelevant that there's only really 1 player essentially lifting the entire 3rd party industry by themselves
I would say PC has more immediate issues with the out of control prices for hardware. Steam hardware surveys still has an absolutely goddamn bonkers percentage of people using 1080p sets and other ancient hardware and that's quickly going to reach a point where a large majority of the market just can't run modern games anymore, and they can't/won't upgrade because it's absurdly expensive to. That's not even getting into how brutally bad these ports are which makes it harder for even high end hardware to run things well never mind more modest sets though I expect this problem to eventually get better. The hardware issue is the most pressing matter because while we pretend PC doesn't have gens the reality is it mostly follows the console market. People tend to upgrade within the first few years of a new console gen to keep up with running modern games, but we're reaching a crisis point where that's not obtainable anymore as "mid level" cards are hitting $700+ levels. If people can't run games they're not gonna buy them either.
