First, I really like the mercenary concept. Rival groups would be a great way to breath even more life into the world and I would love a system where you could compete, assist, or hinder rival groups. For example you run into a Band from another town that paid them to eliminate the goblin stronghold. You either ignore them and try to just complete it first, you agree to work together and split the total reward, or you decide to attack both the Band and the goblins in order to try and collect on both of the bounties that were put out.
Robbery may be interesting but I am not sure I would be too happy if I, as a seasoned, grizzled, battle hardened warrior with 12 similar warriors got a random prompt that a street urchin had blackjacked me and taken my gold. It might be immersion breaking, I would however enjoy little one off “role play lite” events were an event pops up with a few options on how to handle it and it plays out based on your choice and a bit of RNG.
Betrayal should be a thing however I am not sure I like the idea of them betraying mid fight. I could definitely see a system where they break and flee and disappear from your band IE they just never stop running regardless of if you win or lose but a mid fight side switch seems a little out there.
Base of operations, yes completely agree. This would be a great addition in my opinion. Anything that lets us feel a sense of progress and making a mark on the world is good.
Unique characters you have to look for is the first one I completely disagree with. I think the instant you have unique characters you completely change the nature of the game from “sandbox merc game” to “adventure game where you collect your super team to conquer the world”. I think it would be cool to have some extremely rare to spawn brothers to hire that could have higher stats (and upkeep) but unique characters that have a quest to get them would change the nature of the game in my opinion.
Unique items I think would be a great lore building tool. They could have mildly unique looks and those could involve quests to get. It would be fun to travel the world looking for the lost armor of some forgotten king or something.
For your 7 & 8 I think the best bet would be to simply roll those together under the fame and notoriety idea. That would determine how patrols and caravans react to you and eventually you become so famous that even, evenly matched goblin hoards attempt to avoid you.
Mounts would make combat very different and maybe not in a bad way. I am fine with how it is now but I think horses could work if they are balanced properly. They should grant certain abilities, like a charge or something and maybe a trample.
the coat of arms function is a good idea but I don’t see why it wouldn’t be something you could do anywhere as long as you had paint.
11 is a HUGE idea which sounds awesome but maybe extremely difficult to program and control. I could also see it being abused to just force AI factions into wars they cant win so the player could profit immensely
I don’t really have any ideas on top of yours at the moment just wanted to comment and through my support behind most of them.