Why, when somebody already exists in the remote site does it create a new profile?
You can peer with moodle sites you don't necessarily trust that much. It's a key part of the design of mnet -- a single institution could want to run a dozen moodles but there isn't much point with strong roles/capabilities.
The real tear-the-door-frame change happen when different institutions find it is safe to "peer" over MNET.
And any kind of user-merging is a majestic can of worms from a security POV. So no - not there pretty much on-purpose.
... just imagine you peer with my moodle install, and I craft an acct on my moodle designed to "match" your account in your moodle with whatever rules the merging code has... and take it over...
MBWA-A-A-A-A.