Recently, I wrote about four historical settings that would be great for top-down blocks to be based on - now that a fully top-down design is a possibility for a block, Magic's designers should use that to the fullest. Besides, everyone likes some very-loosely-based-on-the-facts historical fiction. So here are three more possibilities:
The Russian Empire. To be quite honest, this one would be worth it for the costuming alone: Think crazily decadent furs, gem-dripping princes, and enormous battleships. The Russian Empire under emperors and empresses like Peter I and Catherine II was the greatest power in northern Europe. This could be the setting for a whole world based on Russia, or just one culture in a world (probably the one portrayed most antagonistically, thanks to the historical and cultural sympathies and backgrounds of the majority of Magic's designers and players, but also because, heck, they were a violent hegemony that didn't want to give up on serfdom). Besides, any excuse to make a Magic artifact that's a take-off on a Faberge egg is a good one. Plus, great place for a naval combat mechanic!
Republican Rome. This would be worth doing just as an exercise of how to differentiate a Greek-based setting (i.e. Theros) from a Roman-based one. In the early days, they were very different, of course, because Rome didn't become Hellenized until it was a very large empire that had conquered Greece. So give us the brutal, noble, stern, agrarian, underdog Rome, the one with its own stories about Aeneas, Romulus and Remus, and the wars with nearby peoples. Maybe make the central characters into Kor, and have it be a kind of Aeneid adaptation with the main people as refugees landed on a distant plane.
Antarctica. Okay, I know, not strictly a historical setting, because no culture has ever natively made Antarctica its home. Even today only a few people live there, none of them long-term, and they're all scientists. But I'm not thinking of penguin history here; I mean taking inspiration from H.P. Lovecraft's vision of Antarctica as the seat of a long-ago civilization of cosmic beings that spiraled out of control. Maybe this could be a way to get the Eldrazi back into the picture, as the reason the plane that a block is set on has been turned into a place of eternal winter.