Your signature certificate is issued by your government (or an organisation working for said government). The seals are created with certificates that are, once again, created by a central authority.
The document exchange is really just a fancy way to store files on your device and send them.
As far as I can tell none of this is decentralised? I don't really see why they would want to decentralise it either, your digital identity as a citizen only exists because a central authority, a nation in this case, validated you to be a citizen ...
As mentioned, correct me if I am wrong, but as far as I can see all of these EU plans are basically just giving each EU citizen a cert that is issued by their government and some nice applications that build around those certs?