I don't think this is what was meant by Adium being possible. At its peak, Adium acted as a single frontend to many different instant messaging networks to provide you a single user interface for chat. Today, we've regressed to a point where this is no longer really feasible; every network requires its own client.
Matrix has bridges, which allow you to send/receive messages to other services like Slack or Discord.
Also, as a different approach, to some degree Ferdium can act as a central place for various messaging platforms even if the integration that Pidgin (and Adium) and libPurple provided is not possible this way. Station is similar and a bit better but is in desperate need of developers. Both are FLOSS.