Will they? Both? Just one of them?

I think they both will.  If not both, then the PS5 at the very least due to its presence in the EU market. It seems that performance wise, the gap might be a bit bigger than some expected between gen 8 and gen 9. Even Halo is rumored to drop the XOne version of Infinite.

With that in mind I fully expect both of them to pass the WiiU easily overall, especially with the Series S being an affordable option as well. I think 20 mil is a more interesting benchmark than WiiU numbers TBH.

By end of 2021 PS5 will easily, XBS/X has a chance, but it would have to perform about 20% better than the XOne did in same period.

The ps5 would have to sell less than 10 million next year, of course it will out sell the wii u by years end.

I'm quite inclined to think both, or at the very least PS5, will, but obviously if supplies will be enough.

I voted both. PS5 is a given. Xbox Series S/X is likely.

PS5 alone.

Series X/S will probavly sell 6-7 million next year.

Both. Combining what both systems do this year and next.
PS5 this year looks like 4.5-5 mil.
XBS this year looks like 2.3-2.6 mil.
So PS5 would need at min 9 mil next year, while XBS would need 11.2 mil.
PS5 no question, but XBS I think can pull through especially if Microsoft advertises the Series S model well and makes it readily available.

voted both. Quick reminder Wii U shipped 13.56 Millions.

PS5 will, Series X might.