It would be great if there was more automation in linking existing users to their other profiles on StackExchange.
and maybe some others just in the Mathematica proposal alone.
A simple fix would surely be that users had to register to commit (but could follow as uncommitted users). That way, it would be more likely that the user's reputation on other sites would actually be recorded and count towards commitment scores.
Another useful response would be to match against email addresses and merge accounts more automatically. I do not know of anyone who wanted to keep their Area 51 involvement separate from their StackExchange profile, and yet used the same email address for both.