@leraje@muntedcrocodile The architecture of their protocol is highly incompatible with the way ActivityPub works.
With their protocol you have got the PDS (Personal Data Storage) that stores your data. Your handle is a hostname, but normally it will not be the hostname of your PDS. In fact you can use any hostname that you have control of. Your account itself is described via the DID that will never change - and that doesn't contain a hostname. This means that you can move between different PDS without people noticing it at all.
In ActivityPub the data storage is on the same host like your handle and your account's URL will always point to the host where your data is located. Moving your account is by far not as smooth and highly depends on the system that you are on.