I voted 2022, but it will likely go for even longer than that. PS4 is going to keep selling just like PS2 did.
Now, I think the OP has half a point. The Pro model should be phased out soon after the PS5 comes out (or maybe soon before). There is no reason to get a "high end" PS4 when a PS5 does the same job only better. PS4 keeps selling because it is cheap. PS4 Pro does not have that advantage. PS5 makes PS4 Pro obsolete.
curl-6 bet me that PS5 + X|S sales would reach 56m before year end 2023 and he was right.
My Bet With curl-6
My Threads:
Master Thread, Game of the Year/Decade
Switch Will Be #1 All Time
Zelda Will Outsell Mario (Achieved)
How Much Will MH Rise sell?
My Bet With Metallox