Your comment has just revealed some interesting things to me, one of them I already had in mind but you gave me the clue I needed to give it weight:
For unique units and bonuses, the creators consider the use of old unique units and bonuses from previous games if they refer to the same unit:
- The English longbowmen, unique English unit in both AoeII, III, and IV.
- The HRE has villagers that carry more resources, reference to Aoe3 was the Villager Cart.
- The streltsy of the AoeIV costs little as it historically was, and is a reference to the cheap Streltsy of the Aoe3, but with the correction that although it cost little, he was an elite soldier.
- The Poleaxe of the Rus Knights is a reference to the battle ax used by Aoe2 Boyars, and also has its reference to various types of ax being used by Rus knights.
- The Full Barding of the HRE IV, apart from having its real reference in the full barding armor of some German nobles, was also already represented as a bonus in Aoe2 for the Teutonic Knights (Barracks and Stable units receive +1/+2 melee armor in the Castle/Imperial Age). The armor bonus to infantry from the Aoe2 is referenced in the Riveted Chain Mail technology.
That being the case, it would not be a surprise if some Civ ideas from other games, which have their representative in AoeIV, also provide new units, unless the references already exist:
Villager Cart.- That being the case, I don’t think the Villager Cart can be added, because it “Already Exists” with the villagers bonus “Pushcarts” that allows them to pick up 40% more resources. Another thing would be that it was an aesthetic variation and when collecting the German villagers they bring out a donkey with a cart, even if it is one of those ghostly golden ones that come out when you build buildings, otherwise it will seem that all the German villagers walked with donkeys.
Teutonic Knight.- Could be, if they consider ruling out a future Teutonic Civ. They were allies of the Holy Roman Empire and several Order holdings were on their territory, but I’m honestly not sure: the HRE Men-at-arm is already an iconic Civ unit, so I’d prefer it not to replace it. Of course, although they formed their own separate kingdom, the order was founded by “German Soldiers (of the HRE at that time)”, and many of its authorizations were given by HRE emperors. Maybe it could be added in a similar way to special units: like the Winguard Guard or the Sultan’s Elephant, that you can create a group of them in some Landmark, but they are expensive and obviously by only being able to build a group, you can’t amass them en masse.
Hussite Wagon.- If we rule out a future Bohemian civ it could be. Overall, the Hussite rebellion only lasted a few decades, and Bohemia returned to be part of the HRE, plus its technology lasted. On the other hand, the Bohemian kingdom’s medieval history has always been linked to that of the HRE, so it is difficult for me to give it its own Civ. Curiously, there is an anecdote about their use outside the country: In fact, Cortéz, who knew the technology of the Hussite wagons (probably because by the time of Carlos V, Spain was united with the HRE) used them against the Aztecs in 1520 while He was locked up in the Aztec palace before the Sad Night, although he named him “Ingenios”. It is not clear if he got the idea from the bohemians (it seems that he did) but anyway he used it and it worked.
Reiter.- It seems to me a better unique unit for the Germans than for the Dutch, because in fact they were invented in the HRE, and on top of that during the time of Carlos V, which is the final portrait obtainable by HRE masteries . That on top of that they had to be “German” to be in the mercenary corps, makes it an excellent option as a unique new unit for the Imperial age. Of course, as a design it could have that of Black Night. Of course, since he uses pistols, old ones on top of that, he should have a lousy range (Range: 3 or 3.5). If they’re going to be anti-cavalry, they might have the same weakness as the Janizaro: 50% more damage from ranged units.
Others If it had been Season III, I would suggest special light cavalry and heavy cavalry with Full Barding… but there are already unique technologies to represent them by giving base units more armor (righteous from the Meinwerk palace), so In theory, for that field they are already fine.