If not trebuchets, then regular catapults at the least. Ballistas, although ineffective against stone walls, would be nice just to shoot down gates instead of having to sacrifice a bunch of men manning the battering rams.
Also, will this mod have armor upgrades this time or will there be some units that feature plate armor in general? Plate armor is worn in the HBO series GoT, but I don't know if Martin mentions the use of plate armor at all in his books. I did notice, however, that at least one unit in your mod features plate armor: the drowned god's chosen unit for the Iron Islanders! Being Iron Islanders, are they the only ones who are supposed to have a badass armored unit, while everyone else wears chainmail? It seems like quite a big technological edge against everyone else, and strange that no surrounding kingdom would adopt the same thing over the thousands of years that they've existed. Is military technology in a basic standstill in Westeros, stuck forever in an early 13th-century time frame? It would certainly add more variety to the rosters to have more units in general, especially ones that are more armored and elite. The Kings of Rivers and Hills submod, for instance, has units with plate armor. Is that sub-mod wrong to feature it?