I don't know if this has been mentioned before, but personally I would like to see more ability to interact with the landscape in the game.
Right now for the most part you can only search around for an ideal place and then build there, hoping no one beat you to it. Players can change forest to grassland, grassland to moor, and moor to heath, but what about swamps, mudflats, and lakes? And what about rivers? If players had the simple ability to remove/place dirt tiles they could fill in rivers and lakes, make islands in them, or even create their own rivers and lakes.
Immersion is a big factor for me in games and when you add a "fast travel" option like the crossroads in this game it leads to people being able to travel across the map with little effort without ever even risking themselves to the dangers outside their forts. Not to mention the possible bounties they may cross in the process. I believe it would be to slow to feasibly travel long distances without the crossroads, but if we could fill in rivers then oxcarting would be viable instead of having to make a raft for every river in the way. Then it could be paved to make a trade route, or maybe dig out a river as a trade route instead. This would also lead to effects of trade routes: central trade hubs and highwaymen, both (whether good or bad) bring random players together to make the game feel less desolate and lonely.
This kind of heavy duty terraforming would have to be a crap load of work of course, but it would coincide with the feel of the game where more effort equals more reward instead of the cheap system that exists now. I know a lot of players will complain, but any dev should know that if you give the players everything they want, there would be no challenge, and without challenge a game is no fun. This kind of system feels easy and cheap to me, and I have fond memories of playing Oblivion traveling from town to town by horse exploring and admiring the countryside until I found out about the fast travel system. Of course I started using that exclusively until I stopped playing the game because it transformed from this large and beautiful virtual world I explored and was a part of to a game grinding quests in a series of towns I was teleporting in and out of, only to leave them if a quest told me I needed to go outside.
The entire system doesn't seem like a solution to the problem of distant travel, and it was probably just implemented as a quick fix in response to growing complaints about travelling.
As for the other terrains, mountains should obviously remain a static terrain since people can't level an entire mountain or pile up and compress enough rock to make one even today in real life. But swamps should be feasible through terraforming and would be similar to digging out a channel for water, except for leaving it more shallow. As for mudflats, well I'm not quite sure how they exist landlocked in this game considering they need a tide to exits in real life, but I'm sure we could come up with a creative terraforming ability to recreate them as well.
There are games with static environments, games with partially dynamic environments, and games with true dynamic environments. Most games are static, where you can't really change anything about the environment, just interact with things in it. Haven and hearth would be partially dynamic in the sense that you can only interact with some parts of the environment (like farming or building on land) but other parts are static and you can't modify (water and the aforementioned terrains can't be added or removed). I think the next logical step to the development of the game would be to make it even closer to being truly dynamic where anything coded into the games environment can be modified. Things like animals, forageables, and ant hills are understandable since they dynamically continue to spawn, but most if not all landforms/terrain would be modifiable instead of generated once at the start of a world and can never be changed.
There's nothing terribly wrong with the game now and I'm just suggesting a route along which the game could be developed further. I'll continue to love the game even if the environmental interaction remains the way it does now. If implemented, it would probably lead to a huge change in the core gameplay and depending on how the game is coded it might take a huge rewrite of the engine, so it is of course entirely up to the discretion of the devs if they want to go this way or not. Thanks for reading and sorry if the post was too long or drawn out.