I rather like replenishment to work like it did in M2 or R1, where you have to march your army somewhere where it can train its elite units and then click a button to say hey! I want replacements. Kind of like repairing ships in S2 worked, I liked that.
I like that also.
I still remember epic battles in R1 where i was leading battered armies with big proportion of mercenaries, whatever was available, just to fill the gaps, at the spot to withstand the next assault.