I've piloted this deck to some respectable finishes as well. 17th at 2015 Vintage champs after losing both of my win and in's being the largest tournament I entered with the deck.
I played snapcaster and brainstorm in that list and they were amazing. I'll never cut brainstorm just because of the power it has to find sideboard cards in games 2 and 3. I don't think I need to explain why snapcaster is good in a deck with ancestral, missteps, stp and possibly flusterstorm alongside dack.
I was testing a list with P.O. recently but I don't think it's quite good enough but mentor is an excellent addition to the deck.
If I were to run this in a tournament anytime soon it would be close to my list from 3 years ago with a sideboard overhaul.