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I think this depends on the Switch more than it depends on the PS5. Nintendo is expecting 24M units for this FY, meaning that by March 2022 Switch should be at 108.8M units. If FY 2022 is at least 20M, then Switch still has a chance at approaching Nintendo DS and PS2 (though I really don't think it's going to get to quite 155M). If there are significant drops (e.g. "THE CLIFF!"), then it wont.
If it gets near Nintendo DS and PS2, then PS5 has VERY little chance at having sales as good. Sony has a VERY good track record with their home consoles. Everything but the PS3 has crossed the 100M mark. So maybe crossing 100M is easy for Sony, but crossing 120M, 130M, and 140M is no easy feat. Add this to greater competition, likely less overall exclusive third party games (I'm sure MS will be stepping in for a piece of the pie more), I just don't see the PS5 doing PS2/DS numbers.
I guess I didn't see Switch getting close to these numbers either.
