I think it depends on the platform. For example, Steam would never federate with Epic Games Store, because that would make Steam users more comfortable with buying games on EGS instead of Steam.

However I think this could change if platforms decide to start integrating more with Discord. For example, if Xbox and Discord decide to share friends lists, I think that would be beneficial for both companies. This might encourage Steam to federate with Discord too. I could picture a snowball effect happening as more platforms start to integrate more closely with Discord, which could eventually lead to a future where all gaming platforms have shared friends lists. (I don’t think it will be true federation though. I think the different platforms would only share friends lists through Discord, not directly with each other.)