So, I'm really feeling this game and definitely want it to get big. I have compiled a few things that could be added into the game. As I haven't played the game yet, some of these features might be already in.
The first one is multiplayer. You could have different mini-games in the game for example Bull riding, etc. However you could also go for a GTA 5 Online style, where is it completely free-mode and you can run around where ever you like!
The second one is, Villages. A bit like minecraft, there could be naturally generating villages and for example a tribe. Now the villages don't have to be actual houses, they could be teepees. You could befriend the tribe, and maybe even become part of it, maybe build a few structures for it and earn "money" (gold, materials etc). But if you want to you could burn the entire village down. This may cause other villages to not like you and therefore if you want to trade with them, they might not want to as you burnt a village down before. However to gain their trust you could bribe them or maybe point a knife at them and make them.
The third idea is side-quests. For example, you might find a stranger in the forest who is stuck. You might decide to kill him, and gain his items, or take him to your house. There could be many other sidequests that could happen.
The fourth idea is inventing things. You know minecraft has redstone where you create new contraptions? Well you could do something like that in Frontier. By that I don't mean electricity. For example, Say I want to create a catapult. I could gather enough wood, build it in a certain way and then when you place a stone in it, then do something to it, it would catapult. Now it would be hard to make the catapult as unlike minecraft there wouldn't be strict rules on how it works. So to learn how to make it, you might find lost maps on the ground which show you how to make it, or maps in a dungeon. So after you have built the thing on the map, memorized it, you could give it to one of the tribes and you will get paid. Then when you come back in a few days, a catapult appears, to show that they used your map!
Those are a few of my ideas! Keep in mind I don't mind if you use any and I don't mind if you don't like them. As I'm not a programmer, I'm not sure if some of these are possible. I will keep telling you some of the ideas if I think of any.