Ideally you would be able to link your (say) github and WMF account. So that if I (as an outsider) start a bug report/patch/etc using my existing github account, and then eventually get a WMF account (so that I can do labs-related things?) I can manage my bugs/patches regardless of which account's cookies happen to be on my machine.
Then you might plausibly allow 3rd party accounts to open bugs, comment on them, etc, but require a WMF account in order to +2 patches, resolve bugs, or other higher-privilege operations. It should be as easy as possible to open and link a new WMF account when a new user starts wanting to contribute more. --scott