Why NOT go to Cathay?  Sure they could do Tilea or Estalia but are they really so different to the Empire?  Not if the Tilean Crossbowmen are anything to go by.  They could do Norsca sure but with the amount of Viking fan wankery out there, that would be quite boring really.  So they’re doing Kislev and Cathay, because they’re less often seen depicted in Fantasy games.  And when it arrives, the Old World will be as fleshed out as it needs to be for the game, because if there’s one thing GW can do right (and let’s face it, it’s not rules), it’s come up with a narrative setting.

I’m not really sure what your point is anymore.  The original question was does the new Warhammer the Old World lore make sense and the answer really is, yes it does.  What we seem to be discussing is why you specifically don’t like a specific design decision to potentially include Cathay as a playable faction, which is not really something I can have an objective opinion on – you don’t like it and there’s nothing much anyone can say about that.  But is it even confirmed that Cathay are even coming to the tabletop at launch?  They have been announced as part of Warhammer Total War 3, but I don’t think that’s any guarantee they’re coming to the tabletop as miniatures any time soon.  Most of the artwork they have teased so far, with the exception of Kislev, suggests to me that they’re repackaging old Fantasy Battle miniatures.  The Bretonnian Knights and archers look exactly like the last iteration of plastic kits.  The undead chariot looks exactly like the tomb kings chariot and so on.  So if they are reusing old kits to support this (which really would make sense as there’s very little wrong with those kits), well there are no kits for Cathay and looks as though they’re already bringing one new faction to the game with Kislev.  Maybe they’re planning Cathay but I suspect it will be at a later date, some time after the release.