Ahh so yes, the fact that the cast is mostly non-white is a thing that adds to the hype. Broadway in the past has had mostly roles for white people - atleast any lead roles. There are, of course, SOME musicals that feature non white actors in the leads, like the lion king, West side story, the king and I, but typically it's all white. (Les Miserables last year casted its first black male as the lead in the Bway production after 30 years of running. It took 30 years for on of the biggest shows to cast a non-white lead. Like it was crazy. And then he tragically died.) And the fact that broadway is a very expensive thing to go to limits who can and can't go (so mostly wealthy people, mainly white people). So there's been a huge disconnect for most of the other races in the broadway world both as performers and as viewers. And unfortunately, it just pushes more of the "white stories" because that's how they'll make money and so it perpetuates the cycle.
Hamilton has a huge focus on telling a story that was mainly about a bunch of old white guys founding America but it tells it through a more modern lens - with more modern music and more modern cast. "The story of America then told by America now." It makes it more representative to what America is today. The try to make it as accessible to as many people as they can through the Ham4Ham shows (10 minute performances of anything with actors in other broadway shows), the lottery ($10- $30 tickets for shows), the EduHam program (getting school kids to see the ply for $10 per student) because they realize that broadway is still not for everyone but they want people who can't afford regular tickets to atleast have the chance to see it. They're very socially aware in a world that typically caters to one race.
To expand a little further on the happenings of Broadway though - it's becoming a very diverse area in the arts and it's really great to see. In the musical area, this past year, they've had the revival of the color purple (all black cast), Allegiance (all asian cast), Fun Home (coming of age story of a gay woman), spring awakening revival (using deaf actors), and a couple more that I'm forgetting atm. On the play side, there's been a lot of other stories that have diversified the stories that are being told too. I know one is about a kid with a learning disability, another one featuring an all black cast, etc. Hopefully they can keep it up so more stories can be shown.