@JeremyECrawford Bladesinger from SCAG: Mage Armor spell and Armor Bonus from Bladesinging, Do they stack?
— The Jeff (@SonicallyScrewd) September 27, 2016
A bonus stacks with anything, except another bonus from the same source. #DnD https://t.co/LRejByH8GV
— Jeremy Crawford (@JeremyECrawford) September 27, 2016
Since Bladesingers are allowed to wear light armor and the song stacks with them doing so. I would say, Yes, mage armor and song stacks, light armor and mage armor would not.