@Stan` and I have actually started a repo for Empires Besieged here: https://gitea.wildfiregames.com/0ad/empires_besieged.  The last change was 11 months ago, but I'm working on things in DE (Guptas and Sasanians; a big thank you to @Duileoga and @Lopess) which will directly translate to EB at some point in the future. So, whether EB becomes it's own "game" or an "era" or an "expansion" or a "release" is up for debate. I personally advocate for a "0 A.D. Eras" concept, where players can swap between eras (Empires Ascendant, Empires Besieged, Masters of Bronze, Millennium AD) and only play those civs, or choose to play with all civs available at once. 

I would love to have such a feature in the game for multiple things, such as wheat fields. But for now, what I mean is that we can have different variations of the structure so that it will look different sometimes when you build one (like how there are helmet variations). 

Yes, that's totally understandable. Regarding the "multiple actor variations", does that mean one chooses, or could it be that the mound evolves from pebbles to grass with time? That would be nice if possible.

Nice catch. Any suggestions for a more accurate "symbol" representing them?

I like having multiple actor variations for the Royal Kurgan. Good idea.    Ideally, I would agree with you. But I think with some civilizations, cultures, factions, that it's more difficult to pick a specific structure (see: Cimbri). So, picking a type of structure is okay, in my mind, especially if it's one of that culture's iconic structures. Kurgans definitely fit that bill! I like @Grautvornix's suggestion of having multiple actor variations.