Sure, the idea is to detach the Actor object (which could be operated by a microserver that consumes almost zero resources, and basically just operates a big redirect table like a link-shortener) from the Service Provider, to be a little more like email (in the use case where you point a domain that you own and configure at protonmail or mailgun or some other provider) or SMS service (in that regulation enables you to keep your number when you switch phone co’s).
We will prototype the micro-Actor in the coming months, but we have no idea how long it would take for implementations like WordPress or forks of Mastodon/Misskey/Pleroma to offer support for this kind of externalized/self-managed Actor. We are hoping existing servers will find it interesting to offer a “service-provider mode” for the nomadic/domain-owning user class, for many reasons. In the meantime, we might also prototype a Fedify-powered server that only allows external Actors to create accounts 