I think the biggest QoL improvement the series can make moving on to next-gen is eliminating load times completely - everything is seamless and you can access the workshop, gathering hall and various areas instantly. Another seamless feature has to be the online multiplayer - this needs to be a quick in and out instead of the quest board SOS searching.
They don't have to mess around with the weapons too much aside from refinements here and there, but I would welcome a new weapon type addition as I'm sure they would nail the gameplay aspect of that.
In terms of environmental mechanics, I'm not sure what else they can come up. I don't think they would bring back underwater combat since people weren't too fond of that. Aerial type combat may be a bit silly to pull off for the series, but maybe? They have the Glider Mantle and air vents in various areas to make you glide up for mounting attacks in World, so they can probably add to these mechanics somehow.
They don't have to mess around with the weapons too much aside from refinements here and there, but I would welcome a new weapon type addition as I'm sure they would nail the gameplay aspect of that.
In terms of environmental mechanics, I'm not sure what else they can come up. I don't think they would bring back underwater combat since people weren't too fond of that. Aerial type combat may be a bit silly to pull off for the series, but maybe? They have the Glider Mantle and air vents in various areas to make you glide up for mounting attacks in World, so they can probably add to these mechanics somehow.