Are you going to use modern warfare?   Much of it lately is based on drone warfare.   Another thing is that the scout troops use light vehicles. From motorcycles to golf carts. Sometimes drones are deployed from these vehicles.  

I wanted to tinker a bit with that, and managed, but maybe not in a clean way (in Win11): Went to AppData\Local\0 A.D. Empires Ascendant\binaries\data\mods\public. Unzipped public.zip, and renamed this one public.zip.old, just in case. Went to art\textures\ui\session\icons\resources. Pasted a lettuce on top of the meat in food.png.cached.dds. Renamed that file food.png (this step took me a while to figure out, and why I think I'm not doing things cleanly). Zipped all contents of \public in a public.zip file, and moved that up alongside public.zip.old. Result (you would need to take care also of other meat icons @NiRa Muso MIOZOTO, like the ones indicating food cost):

I think they should, just like building capture, not to overcomplicate things. It would automatically be just more useful for some than for others, particularly since civs that don't build complex ones would be usually more mobile.

I'm not sure every civ should have the ability. But at least the civs that actually captured them historically could have a technology to unlock siege engines. https://tyche.univie.ac.at/index.php/tyche/article/view/5047   This article at least argues for them being Scorpions but the original source is no that clear in any case.

I see. The issue with real time MP (if you consider to add that at some point) is, obviously, that if some (or many) player(s) are engaged in "battle map", for the rest still in "campaign map" time would need to pass "too slowly" (not to lose sync). If some players abuse this, it could get quite boring for the others, so I thought maybe each could have a "focus" bar, depleted while they are in "battle map", regenerated otherwise (that's a simple explanation, this could actually depend more finely on chosen speeds).   Hopefully you can get that from Parts II and III of Thoughts on the Athenians, already sourced from plenty of the most important books and researchers on these issues