The whole Series S justification hits a big wall which is the lack of disk drive. You want a buget console but have to pay games at full price and cannot buy used games or sell your own games is the opposite of a budgetfriendly console. 

And yeah you can have the Game Pass but will have to pay every month + the games doesn't belong to you. 

So IMO the Series S fails at several levels and won't nearly sell as much as the Series X. (1/3 or even 1/4 as I believe the current numbers are heavily tied to the stock issues of the Series X)

For the record, my justification for thinking the Series S/X will sell poorly is a similar-ish reason to (one of the many reasons) why the Wii U sold very poorly. A bad name that makes people think it is a mere "Xbox One.25" instead of a true next gen console.

Granted it will sell way better than the Wii U, but I can see the Xbox Series selling only like 30-35 million or whatever, especially if there are only few exclusives. In fact does the console have any exclusives at all as of now?

What's a Wii U? Never heard of it...

Yes, the bad side effect on the full-fledged XBSX made me totally overlook XBSS' biggest flaw, the one that directly affects it. MS could mitigate it only conceding the freedom to choose 3rd party digital marketplaces, to at least be able to look for the best price on new copies, but I guess it wants to push Game Pass (or any other 1st party GaaS it will launch in the future) more than anything else.

Ps5 will outsell every Nintendo System ever released with the exception of DS, i know hard to digest here but get ready for some bad bad years for Nintendo Fanboys once Sony gets the Stock Right.

& yes it will Crush Wii U numbers by the end of 2021 which were pretty damn terrible.

Xbox? Well depends, Series will probably sell a tiny bit better than One but it´s not even a lock yet, Brand has been damaged beyond repair and they don´t have Franchises like Nintendo or Appeal to do a major comeback.

Nintendo has the IPs and the System to do gargantuous numbers, MS let Halo slip with 343 & Gears doesn´t do much in this day and age.

I think both will but it'll be relatively easy for PS5 to do it, I think it may be more challenging for Xbox to do it.

Edit: It also depends on how quickly MS and Sony can get stock normalized, so far both are still out of stock at most locations

Voted Both will surpass by end of 2021, i still have my wii u.

The PS5 would need more or less PS3 level sales for 2021 not to beat the Wii U, seems unlikely. The Xbox is more of a question, we really don't know what it will sell. The Xbox One has sold decently, but never really well in any one region, and MS' gamble with possible driving a slight wedge between developers and end user in releasing a considerably weaker option for their fully digital alternative has yet to show results. I think the Xbox Series S will prove to be more a problem than a boon to MS, when all is said and done, and that they might have trouble delivering enough Series X units to those Xbox fans who want the best version of their games.

They'd have to sell really poorly to not do it.

I think the PS5 will do it easily. The only scenario I can think of where the PS5 doesn't do it is if something goes terribly wrong with their production line. The XBS, on the other hand, I really don't think it can make it, but I would love to be proven wrong.