PT12 sessions in PT11 questions

I realize PT12 just came out today and I've read over the list of 'improvements' and I wonder about something: with all the changes in routing and such I wonder what will happen when someone does a fresh session in PT12 and either themselves opens it up in PT11 or sends it to someone who only has PT11. Will PT11 start throwing errors and people go arrrrrghhhhhhh!!!!!!!!! and the air turns blue? It would be a shock if Avid has taken this into account already.