From the (un)-archived discussion at meta (http://meta.wikimedia.org/w/index.php?title=Wikimedia_Forum&diff=next&oldid=3619272), [[User:JohnnyMrNinja]] writes (in part):
I am proposing that account unification be completed for all eligible accounts
without requiring the user to take any additional steps. This would make UL the
rule rather than the exception that it currently is, and bring us closer to the
goals of universal watchlists, recent changes, interwiki page moves, etc. This
would be especially helpful on Commons, which has so many images that were
originally uploaded at another WMF wiki, enabling better attribution without
interwiki links. I propose that it be carried out as a one-time process rather
than a continuous automatic software process, allowing users to still adjust
ULs as they see fit.
[...]what I mean by "eligible accounts" was all accounts without existing
conflicts, as these can be taken care of by an automated process. Accounts that
have conflicts would be unaffected by this specific proposal. Conflicts could
not be solved by any automated process, as each case would be different.
Looks like it has enormous support on meta. I'm not sure about the ins and outs here, so I'm going to add people who I think know more as well as post this bug to wikitech-l.