Isn't that true of D-Bus as well? I mean, maybe it's just semantics, but if you're going to use the word "nominally" (read as "it claims to be") when saying it's network transparent, D-Bus is certainly "nominally" network-transparent as that's an advertised feature of it.
In contrast, SunRPC is RPC, so network transparency is a given. The reason I said "nominally" is because in the case of SystemXVI, having proper distributed service management (not a goal at this point) would require more than that.
Search for "TCP".
(A shared secret sent in plain text is not security).
Which is more or less what CoreOS's `fleet` already does on top of systemd. They used a different protocol for remote communications (etcd, ie. HTTP+JSON) vs. local, which I guess can be a sensible choice as requirements are quite different.