Generalized as in it can be used to build a fortress/city/farm/whatever and fill a (chunk of a) table.
So generic buildings basicly. Houses, towers, fortified walls, factories, etc.
So for example, the Rohan stuff for LOTR. Its a bunch of generic houses, so you can put a couple down without it looking weird. There's some walls and towers to make fortifications. And it's fairly straightforward to bash 2 models together to create a big house, or to make some simple terrain yourself like fences, a well, a shed etc. to flesh things out. It's very straightforward to build a village. Sure, it's going to be a Rohan themed village. Or maybe a "human" village if you throw in a gondor building or two. But at least it's a whole village and not just a bunch of random pieces of terrain.
However, in AoS we get stuff like a magma forge, or a charnel throne, or our realm engine.
You can't build a village/city/whatever out of those. The best we can do is just a random collection of nonsense.
Hell, most AoS terrain is so unique that even putting down multiple pieces from the same faction quickly looks weirds (e.g. 3 charnell thrones next to eachother looks kinda dumb)
So yeah sure, practically speaking it will probably be specific to some faction (let's face it, probably the humans/sigmar), or maybe a handfull of factions (give each grand alliance some generic terrain, maybe with some small addons? E.g. chaos terrain with some bits to theme it for each major god?) since selling enough scenery to build cities for 30+ factions isn't going to be feasible. But it'd be nice to be able to build cities/forts/villages/whatever.
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