I don't see Sony making any moves towards SEGA. They might be one of the cheapest big japanese publisher out there, but they also by far in the worst shape when it comes to their ongoing franchises.
Sonic, Persona, Yakuza, Total War; that's not an exciting lineup of franchises you would get for $4B.
Strategically, Sega aligns more closely with what Microsoft is hoping to accomplish, although it's not "perfect" for either. It has the Sammy Amusements side that neither company is interested in. However, Sega Europe is very PC focussed - Sony is expanding into PC, but it is not expanding into PC-exclusive games like Total War and Company of Heroes. For Microsoft, PC GamePass is another pillar of their business they're trying to grow. Relic, a Sega studio is making Age of Empires for them (PC only at launch).
I don't think Sega is going to sell soon though, to anybody. The games side of their business is doing great, the amusements side is doing poorly, selling the whole company is messy to prospective buyers, and it's not clear why they'd want to sell just their golden goose and keep a dying company. A merger with another Japanese company is no less likely than a sale. The last big wave of game company consolidation in Japan in the 00's was largely beneficial for those involved, and they'd probably benefit again, albeit it would be tricky to come up with good name for "Sega-Sammy-Square-Enix Corporation" or whatever.