The pops concert that is the Last Night of the Proms invariably culminates in the ritual “Rule, Britannia!,” led by a superstar with the flag-waving participation of the 5,544 lottery winners inside the hall, plus legions of live-feed watchers gathered the length and breadth of the United Kingdom. This year, the luscious American mezzo Jamie Barton does the honors. An original costume concept is de rigueur. Can she top Admiral Lord Nelson lookalike Sarah Connolly in 2009, the Maltese footballer Joseph Calleja in 2012, or the Peruvian Juan Diego Flórez, in full Inca-emperor drag, in 2016? (Check them out on YouTube.) Only time will tell. —M.G.