I expect that surpassing the milestones of those older consoles will occur at an accelerated rate now that stock issues are a thing of the past. I dunno if the PS5 is gonna get anywhere near the PS2 lifetime sales, but I think it'll handily crush the PS3 and PS4. A quick check on Wiki shows the following lifetime sales in Japan for the PS consoles:
PS4 - 9,431,894
PS3 - 10,469,971
PS1 - 19,411,000
PS2 - 24,420,000
If I had to take a random guess, the PS5 will land somewhere in the region of 15 million lifetime sales. Indications are that Sony's planning to move an absolutely ludicrous amount of consoles next FY and I think a good many will be sold in Japan.