The PS5 will supposedly be almost twice the thickness of a PlayStation 4 Pro and has a design that is completely different to everything that has been predicted so far according to a Sony "insider". Sega may be planning a new console release or might team up with Microsoft in Japan for a "Sega Series X".
https://www.notebookcheck.net/Next-gen-console-rumors-PS5-will-be-twice-as-thick-as-the-PS4-Pro-huge-Sega-scoop-could-point-to-a-new-console-or-even-a-Microsoft-team-up-for-a-Sega-Series-X.467526.0.html
I don't think its microsoft theyre partnering with at all. If its a console, its most likely independent or Sony/Nintendo. Its most likely a retro console and/or games.
MS is more financially able to do this than Sony or Nintendo, but who knows what will happen. MS definitely needs a foot in the door for the Japanese market, because they don't like American consoles at all.