As far as treating the information as canon, and the definition on MNFF, that is also being currently discussed by the moderators. As the backstories are all written by JK herself, they are canon and will be treated and looked upon as such. As the information is released through Pottermore, the moderators have a reference thread to refer to so they can check quickly to verify the canon information from there.
My question (more than suggestion, unless it triggers a debate) is whether we still ought to stick to the way canon is currently defined at mnff. Writers here are going to use that information to be inspired anyway, but will it have any effect on warnings placed on the story that utilises information from Pottermore? Not canon or canon?