One thing I see as an ancient PC Gamer is that Activision also sits on one of the largest hoards of IPs. Not just "cool" IPs from today's games (a lot of people are mentioning Activision's odd/bad stewardship of Blizzard, of course), but Activision bought a lot of the classic publishers in its history as a massive M&A shop. The legacies of Infocom, Sierra, Knowledge Adventure, Davidson, and many more both well known and almost forgotten to history developers and publishers have all been locked into Activision's forgetful vaults. It's such a huge swath of classic PC games. Some of that catalog Activision eventually allowed onto at least GOG (with GOG allegedly doing a lot of the preservation work to make them run), if not Steam, but there's still so much of gaming history that Activision has either claimed to have lost (No One Lives Forever, as one commonly discussed franchise) or just seems disinterested in the IP they own because they can't figure out how to build mobile games from it.

I don't know if Microsoft will be a better custodian of all that gaming history, but as the company most synonymous with the PC today, maybe they will. (If so, among other possibilities PC Game Pass could get very interestingly different from Xbox Game Pass.)