I think ultimately, second party will be a large driver of the acquisition spree. With the exception of Nixxes, all of the studios bought in recent memory have been former second party. This is because in part Sony owns the IP of these studios and in part because they have a strong working relationship. We know for example MS supposedly offered to Housemarque but they chose Sony.
Now, with big public firms, that's not a fight I'd want to risk, given that MS, NetEase, maybe even EA and definitely Tencent will be ready. We've seen this happen with Codemasters and Leyou. The shareholders for these large firms in particular will want the highest ROI which means paying a premium at best and outright losing to the competition at worst. With all of this being said, here are the firms I think have potential given their relationships over the last generation and known relationships beyond.
- Lucid
- ThatGameCompany
- Giant Sparrow
- From Software (if Kadokawa will sell, bidding war risk. Also possibility of buying Kadokawa outright and get Spike Chunsoft too. Bulk of business unappealing to MS, may attract Tencent)
- Arrowhead
- Quantic Dream (Although based on rumours unlikely)
- Supermassive (with stake acquired from Nordisk)
- Valkyrie
- VooFoo
- Heavy Spectrum
- Plastic Studios
- Q-Games
- Alvion
- Bungie (Sony published Destiny in Japan. Risks bidding war. Price supposedly 2 billion)
- ClapHanz
- Creative Vault
- White Moon Dreams
- Impulse Gear
- Mass Media Games
- Wish Studios
- First Contact Entertainment
- Monstars
- Resonair
- Flavourworks
- Other Ocean (Including Digital Eclipse)
- VIVA Games
- IllFonic
- Camouflaj
- Darkwind Media
- Iron Galaxy
- Haven
- Probably Monsters (Firewalk)
- Deviation Games
- Kojima Productions (supposedly working with MS)
- Remedy (Public. Possible risk of bidding war)
This list is not exhaustive. As shown by Nixxes, a 1:1 second party status is not needed (although they did help on Shadowfall). Additionally, third parties with strong working relationships like Arc, Ember Labs, Oddworld Inhabitants, Counterplay, etc. are 100% on the table, as are some studios we may not be thinking of, but I think this may be a good jumping off point.