The scenario of companies opting to host instances may happen, just to try to jump into the bandwagon, which could imply they could/would at some point start to run ads but I’d risk the instance would quickly be defederated and/or turned into a hell pit.
But the notion of seeing an instance being run by GOG, Valve/Steam (not a client or fan but I aknowledge they have put a lot of work towards Linux and gained a lot of support because of it), AMD (fanboy here, give me a pass), RPi (I am aware of the shady turn they have undergone) and other companies that have some degree of respect in the Fediverse could be interesting.