I will restrict the number of elite units that can be produced by other means of course, but I think it will just cause the player to gather them from all around the country and form a doomstack.
The player has no combat input (you send the army to fight, end the turn and pray for the best), possible exception are some orders adjusting the behavior of the army, for example when to retreat.
I would love some feedback and of course more ideas on the matter, I'm sure you have some.
I sure do. Like you I had the EU mechanic as a sort of baseline when thinking about this. As a general rule I wanted a little bit of a rock-paper-scissors feeling without having too much "this unit has +50% against that unit". Less gamey but the same result basically. Also the consequences should be relatively easy to understand for the player, as you said.