To be honest my idea here is something that is something closer to the changes made by a mod rather than a full rework of the of the original game. From the a more realist stand point I think more Royal Embassy HC cards are most likely the way forward.
I do enjoy this idea and I really thought something like this would have been introduced before they added Rangers into the game to give the British a rifle unit (Gurkha) for the late game, although its probably not as needed now. But I still would like to see Gurkha and Jat Lancers make a greater appearance in the British Civ.
I just think it would be cool if some of the European powers could get units drawn from their colonies to reflect the benefits of having an empire in the Victorian Era.