I think it's going to be more muted than before.
Nintendo fans are happily set with their switches.
Xbox has very little momentum at the moment, exclusives have trickled out in recent years for them and with very mixed reception. Their big feather in the cap is 'best console multiplat', but it hasn't translated to huge sales, and also overlaps with doing it better still on PC anyway. Gamepass and Streaming, ehh. Good options, but not compelling ones.
PS has excellent momentum thanks to years of well received exclusives. The fact that PS5 is BC (and almost certainly 'enhance' for PS4 games) means PS4 customers with PS+ and physical+digital libraries/friends will have the easiest way to just go PS5 if they're interested in a 9th gen box, as they keep everything they've paid for. Just like an X1S/X1X customer may decide to go Xbox again because their games/services will carry over.
The price is going to be why I think 9th gen will have an amazing holiday performance before dropping down substantially afterwards. PS4 and X1 both basically sold out first Nov/Dec. Diehard fans will pay whatever the cost at first. But once the initial hysteria passes, reality sets in. As 2014 progressed, sales for the $499 X1 hit the floor, $449 didn't save it, and despite doing 'better', $399 PS4 was basically just steadily plodding along as well until the fall of 2014.
Hugely popular IPs like Fortnite and Minecraft run on toasters, so that's another thing where it will be tougher to push $500 consoles beyond the enthusiast space.
Anyway, overall I expect PS5 to lead, but not at the same pace to begin with. Xbox to do 'better' than X1, but not by a lot, and overall a bit muted 9th gen until mass market pricing hits AND 8th gen is no longer getting supported. PS4 will still be a major force in 2020 and a solid presence in 2021 simply due to economics.