From reading across multiple forums, being 'invited is promising. But some people have also been accepted without being 'invited' on Acorn prior to receiving an official letter. It seems kind of confusing.
I talked to my friend who was wait listed for another UofT program and their Acorn was not updated. Then I asked another friend who was accepted into Munk for European and Russian studies and their Acorn is updated. So all in all, I am happy to see 'invited' but I'm waiting for an actual legitimate letter for real confirmation.
I guess letters will most likely be sent out next week, if things are the same as last year