For now the devs decide to go Sci-fi but at this stade of the game if someone comes with good idea devs can (maybe if you are persuasive enough :P) agree to change to another style, but come on , we can't switch from sci-fi to heroic fantasy :P
but a switch to steampunk should no be hard , the future can be steampunk :P
i will advise you to not do a total work without showing first some drawing to show you ideas (they can be rejected) so don't rush at work , post some drawing in the forum first wait for the ok of the devs and then go.
IMHO we must follow the rule "small is beautiful"
let's not see too big but beautiful why starting tons of buildings/chars design when they will be ugly , let's do few but very well !