Well they had mist in Black Forest and it wasnt that bad... I think they could kick it up just a notch or two and it would be great. Not like fog-on-the-ocean or Mountains-Blizzard bad...

Or potentially just decent fog all the time, but weather effects like blizzards or rain where the fog rolls in extremely thick for a period of time.

Im thinking building bases in Mistlands is going to be a real visual treat tbh
Take your lodges and long halls and castles and drop them in a misty biome where they jut up from the fog, torches and lanterns aglow