The next DA title should definitely feature a day/night cycle. it could add some dynamism to the ambience of the maps.
It depends on the scale of the story, and I think it works better if you're confined to one more homogeneous area. If it's similar to DAI and DAO, I'd still prefer the variance offered by discrete zones. That said, it's just a different and equally valid approach. I only played the first 20 minutes or so of B&W last night (enough to get to Toussaint and complete the very first enemy encounter), and it's incredibly beautiful - just as Kaer Morhen and Skellige are incredibly beautiful - but it's still only the third biome we've seen in the game. There's something to be said for variety (and I think it's mandatory in a continent spanning story like DAI).
There may not have been dynamic weather and lighting in DAI, but the environments were deliberately crafted (and well-crafted, in my opinion) to convey an appropriate mood, and the end result is that the weather and environmental effects look just as good (sometimes better) than the dynamic weather in TW3.