I think generally it's not a good idea to think of Sega and Microsoft as the exact same company in the exact same situation.
Sega was going bankrupt, they had no choice but to immediately pivot or die. Microsoft is not remotely in this kind of bind.
Sega had a sizeable install base but with no way to keep them spending on Sega product, meanwhile Microsoft has sold at least 30m units of Series consoles alone, they can keep monetizing that audience for subs, games and accessories for far longer than Sega ever dreamed of.
This is why I think Microsoft will keep going in some way or some form in hardware. They will not leave unless something drastic happens with the spending of those 30m console users.
Valve has already been growing the Linux side and will launch their SteamOS line of devices ahead of Microsoft. You should google why SteamOS exist, then you'll understand why it might be risky to help them enter the living room.
I know what SteamOS is rofl and I know it's coming to other devices. You're missing my point entirely.
What Microsoft wants is for Valve to have the majority of its business still conducted on Windows. If they just let them be and let them grow SteamOS as they see fit then Valve will eventually be in a position to start dictating terms or even driving non-Windows OS adoption.
Right now Valve's business is
at best at a 90:10 split between Windows and SteamOS, Microsoft wants to keep it that way as long as possible, one way to do this is to "allow" Steam to start selling to the Xbox userbase directly.
Does this potentially torch Xbox? Probably yes, but it also keeps Valve reliant on being friendly to Microsoft in the medium and long-term.