A great piece by Paris Lees - which thinks about and asks why this doesn't happen, though the header makes it sound like it's going to be another 'Only A can play A!' foot-stamping whine.
Far from it...
Friends in casting tell me their first choice is to cast trans people in trans roles nowadays. What a shame we don’t have more established trans actors, or at least none on which Hollywood would gamble a big-budget film’s success. Until we encourage acting talent from diverse sources, that seems unlikely to change any time soon. So yes, watch Dallas Buyers Club and by all means enjoy it, but, when Leto’s on screen, keep an eyebrow raised.