Just had this thought in my mind. What would happen if as has happened before, the royals get captured and its up to Starlight and her friends to save Equestria but dispite all of their efforts, they still cannot overcome the villian. In desperation, they resort to extreme measures. Sunburst would most likely be aware of the consequences of the alicorn amulet, but faced with the fate of Equestria, the royal family and more personally, the one pony he cares most about in his hooves, I’d like to think he would use it, but only as a last ditch effort.  
Having the most knowledgeable pony in magic in Equestria having the power to fully use it would be a sight to behold. I’d think it could be good for a season finale or premier. But that’s just my opinion.