Fair enough, though I can see this being harder to design and code than most things.
For instance, who carries the banner? Is it a Western-style banner or a Japanese-style sashimono? Can they also carry a weapon? If you've got like 5 troops, does that mean that you lose 20% of your fighting strength when one of them carries it? Is it for every combat or only army combat?
Do you want a banner in each formation? Well in that case we first need to have actual formations first instead of - for instance - just one "formation" of all your infantry together.
I don't knock you for trying to keep the flame of actual banners in Bannerlord alive. I'm just saying I'm skeptical about its logistical feasibility when there are so many other basic problems with what we have.