I don't think it would be too hard to implement good controller support. A lot of sticky targeting as default with the possibiliry to aim freely. Grid based inventory works too you move one grid / click.

Now should Larian do it, I think it's up to them to decide. If they go for it, it should be done properly and resources need to be spent on this. There are enough bad ports as it is.
Personally I think the current UI needs more work and implementing support for controller could be done at the same time.