This idea is simply awesome. I don't know how to make it happen, but the
Varangian Guard needs to be available for Justinian. Purple berserkir must wind up in this game. I'm not sure what their bonus would be (they served primarily as body guards, but also functioned as the ace up the sleeve as reserve warriors only unleased in clutch situations) - Drill, Garrison, or heavy defensive bonuses would probably work. Maybe Justinian would need a city north of the Black Sea in order to build them?
The Gustavan military of Sweden relied on the
Hakkapeliitta of Finland, which could be Pistolier replacements only available in Finnish cities. They were known for their speed in battle and were used for scouting - giving the already lethal pistolier a 4th movement point would be horribly unbalanced, so maybe free mobility promotions would make them slightly more dangerous (hills mean nothing to them), without making them stronger. The Russian hills and forests would be much easier to tear through with these. They could also be utilised as lethal forward light field cavalry this way without hills/forests slowing them down (start the turn on the same tile as infantry/siegecraft, attack 2 tiles forward, fall one tile back; infantry advances one tile forward & cavalry finishes turn on same tile as infantry).
Conditional UUs would be awesome, and I'm sure each civ could gain at least one extra unique unit - the Pecheneg/Kipchak horsemen could be employed by the Byzantines to attack Bulgaria while Bulgaria employs the Cuman horsemen to attack the Byz (these are already sort of implemented by barb horsemen, but I think the concept could work). Another angle to approach this from is as a great way to implement minor civs that can't otherwise be implemented in the game, and make them available to any civ to hold a given province - Mamluk soldiers could be trained in Egypt by any nation holding ground there, finally providing Mamluk presence and hopefully quelling debates about Mamluk representation in the game. Highlanders could be built by anyone holding Scotland (Spanish- or French-backed highlanders causing trouble for Protestant England? Awesome.). This might make less historical sense, but be easier to code. If possible to code without much difficulty, an additional requirement could be added to keep universal UUs somewhat historical (IE Mamluks require Islam as state religion and/or present in the city, so only Arabia, Ottos or Indies build them on their own, and no Mamluks come from Byzantine Alexandria . . . unless of course an alt-history loving Islamic Euro human is at the helm).
I don't think this would break game balance too greatly, as most of the UUs wouldn't be well utilised by the AI - with the Otto's unit spam, what're a few more? English shipping Scots to the Continent? Not likely. Russia is too backwards to ever be a real threat to the human, Cossacks or not. The human is the only one who would enjoy the feature, and the human is the only one who counts, really.
I'm sure it would be a pain to code, but this kind of idea would make a stellar addition to an already stellar mod.
