I think there's a lot of room for historical MUSHes. I like reading history and RPing in it can be great. That said, I think it's hard to make the games feel authentic since people find it distasteful and backwards to RP as someone who acts like they're from the time and place the game is in.
And I don't just mean cases where it's the norm to be racist or sexist, either, although that definitely applies. Not only might it be a reach for you to regard women and non-whites as your peers, which everybody knows goes against current sensibilities, but you've also got to believe the weird folk wisdom of the era and region. Things like digging holes causes rain and rubbing shit into your wounds will heal them might have to be something your character won't just believe, but will get smug about if some other character challenges it. Imagine having to get unironically condescending IC because someone told your character that the number "zero" exists or that there might be an ethical issue with bum rushing the Balkans for more Janissary conscripts and nubile sex slaves.
And you can't let too many people be skeptical IC, because if you let people do it, everyone will do it in the interest of not RPing as a Bad Guy or a moron. On top of this, basically all historical settings more than a century in the past have this sort of thing going on.
