distributed WKEs

I've got a question about the APEX, relative to implementation.  I realize
that APEX is still at the specification stage, and I apologize if I'm
jumping ahead.  

How does one implement scaleable, redundant Services which connect with
Well-known Endpoints?  E.g., to allow for greater scaleability and to
eliminate any single-point of failure, I'd like to be able to attach
multiple instances of, say, the Presence service.  The Presence
specification appears to promote this: "APEX services are logically defined
as endpoints but given their ubiquitous semantics they do not necessarily
need to be associated with a single physical endpoint."  Does this then mean
that it's legitimate to associate multiple physical endpoints with the same
endpoint ID?  Is this a special type of attachment that is legal only for
WKEs?

If that is the case, the Presence Service is logically a single endpoint,
but physically might be distributed across multiple processes.  Assuming
that the Service is stateful (which I believe is true of the Presence
Service), how is it envisioned that the service would operate internally?  I
can think of ways to implement such a distributed service (the instances of
the service could consult a common datastore, or communicate with each other
to synchronize state).  But if work has already been done in this area, I'd
like to leverage it...