I increasingly suspect there are false dichotomies here. A user need not take full responsibility for their personal server/instance on the federation for them to truly own their data and presence. They only need to own a discrete component in the network that is easily moved and that contains their own personal information and identity. This component could just as easily be hosted on a large cloud service as it could on a bedroom Raspberry Pi, and, if truly nomadic, moved from being on one and then the other as is necessary.

It seems to me that most architectural thinking on this point fails to consider anything other than the "hardware" or server, in more or less traditional network terms, when, it seems to me, the issues concern the presentation and address-ability and mobility of the user as a discrete object.