Larger massive multiplayer capability was one of the features Google was touting upon Stadia's launch:
Over time, Buser [Google’s director of games] says we should not only see additional exclusive games on Stadia, but also cross-platform games doing things on Stadia “that would be impossible to do on a console or PC.” Instead of dividing up virtual worlds into tiny "shards" where only 100 or 150 players can occupy the same space at a time because of the limitations of individual servers, he says Google’s internal network can support living, breathing virtual worlds filled with thousands of simultaneous players. https://www.theverge.com/2019/6/6/18654632/google-stadia-price-release-date-games-bethesda-ea-doom-ubisoft-e3-2019