It will sell below Wii U for sure but because it won't be a closed platform like the XBSS/X, it means that big sales aren't required for success. Steamdeck has been a huge success even though it sold a tiny fraction of Switch. Different business models entirely.  

It won't necessarily mean success in Xbox's context. Valve has a major platform in Steam that is actually assisted by the SteamDeck. Whereas Xbox going PC could end Xbox as a distinct platform and have the majority of its users move to Steam.

I wouldn't call SteamDeck a "huge" success. But both it and "Xbox-PC" increase the popularity of Steam. For Xbox-PC to be successful, it'll need to retain a large userbase and generate a ton of money from platform fees.

MS's equivalent of Steam is Gamepass though? You could argue that is also a major platform/service? I disagree with it needing a large userbase to be successful. It's job is to be a compliment to Gamepass, exactly how the Steamdeck is a compliment to Steam. If steam deck fails Steam still stays alive but, it's just not as successful as it would have been without Steam deck success. If the next Xbox-PC fails, Gamepass stays alive too, just not as successful as before. See? It's very different to current sales model where, if the console dies the online store dies with too. 

GamePass isn't Steam's equivalent. Major services were their own thing that used complement existing platforms (we don't know for instance which between PS+ and GamePass is more profitable per user or in total). GamePass's profitability remains questionable, and it's not going to replace the 30% tax, most of which pure profit.

It might evolve to a service big enough to beat "current Xbox" in most relevant metrics. But all I'm saying is that Xbox-PC selling like SteamDeck or even multiple times more doesn't automatically make it a success. Other factors will need to be considered.

SteamDeck had no negative implications on Steam whatsoever, it was always going to be a net positive just like Playstation Portal. Xbox-PC clearly has negative implications on Xbox, calculating the impact is inherently more complicated.

Does it? What are they because I don't see any negative implications of Xbox-PC. Everyone on this website (even hardcore Xbox fans) are saying that Xbox has evolved into a service now. It's more of an App that you can run on any Xbox/windows device. That + Gamepass. Standard Xbox console hardware has been selling terribly for awhile now but the windows App and Gamepass still survives. 

So, what are the negative implications or consequences of the Xbox-PC not selling? If hardware selling poorly was able to have negative consequences on the Xbox App or Gamepass it would've happened by now. There aren't any, it's just not been as successful as hoped. 

We don't have Microsoft's data to make any complete conclusions. And things could always get worse.

The most obvious negative implication is further loss in user spending outside GamePass. The 30% cut is VERY important for platform profitability. Moreover, the vast majority of GamePass players are on Xbox hardware which you say is selling terribly. So future Xbox hardware being expensive and unpopular may gradually reduce or stagnate the numbers of GamePass subscribers when people move from Series XS. GamePass has been available on PC for many years and yet only a tiny fraction of PC gamers are interested in the service 

GamePass just isn't an equivalent to Steam no matter how people want to spin it. It might evolve to something more significant, but so far it's not really more relevant than PS+ which is a small part of a greater platform. PS+ is actually more successful in that it doesn't seem to be particularly hurting traditional sales which are still close to Playstation's record. GamePass needs to see a huge growth to make up for the decline/death of their standard platform.

There's a leaked Zen 6 + UDNA APU 36 GB/80 CU design, which Kepler believes to be for the next-generation Xbox (or "Xbox PC"). That is not coming in cheap.

It's clear that it's poised to compete as an alternative to mid-level gaming PCs rather than at console pricepoints. Honestly, it kind of makes sense there: even $1000 for 5080-like performance is not going to be a bad deal, even ~2 years for now.

Yes, and they're never going to share that with us so why even make that point? I know vast majority of people on Gamepass are on Xbox, but MS doesn't act like it values console GP users. It makes them pay more for the same service. They treat console players badly in general. They told everyone starfield couldn't run at 60fps because of complex systems like the sandwich collecting stuff, and then released a 60fps path months later. Your argument is valid in saying that MS SHOULD value it's console player base, but they clearly don't with the decisions they have made. The proof is in the pudding and we don't need access to the data as you keep saying. 

A good reason for Sony to learn from the PS5 and launch with PS6 exclusives from the get-go, much like Nintendo did. They (Sony) claimed they needed to support the PS4 due to the size of the install base, but clearly, Nintendo has proven that to be faulty logic. People will support your new console right away if you give them a reason to.

Demons souls remake? They did have launch exclusives. Also, Nintendo has proven that supporting an older system after launch is faulty logic by launching Metroid prime 4 on an older system?