Sorry I have absolutely zero modding experience..
Basically I don't really see the need for a huge mod this round. If the simple mod becomes popular, then it should be no problem getting help to improving it. Taleworlds sometimes also implement good ideas in mods, so who knows?
For this simple thing to work 2 things are necessary as I see it
1. A leader class, maybe he could be elected with the poll system already there. It would be easy to throw bad leaders at least. And not everyone wants to be a leader, so hopefully the poll wouldn't be spammed too much.
2. Three types of special arrows, only available to the leader that are:
A: very visible and/or transform into colored flags of different kinds (Faction specific symbols!)
B: have unique sound (faction specific! I'm thinking Horns here! Not violins or UT-sounds. HORNS!)
C: that disappear when the next arrow of same kind is shot, or only last a short while like 20-30 seconds
That's all I would wish for now. Of course I'm thinking PUG games here. For Clan matches you don't need the idiot proofing, and the leader wouldn't have to be electable etc..
Now don't go ahead and make the mod too big! If you want, I can help with images(textures?) for the flags.