The Witcher 3: Blood and Wine is a graphical upgrade over the base game

I hear Toussaint is prettier then Skellige this time of year...

The Witcher 3: Wild Hunt is predominantly a very beautiful game. Is it on par with the trailers that were show off at E3? Not quite. But CD Projekt Red might have just gotten there with the upcoming expansion, Blood and Wine. 

Senior Environment Artist Len de Gracia told Eurogamer the following:

"Generally it is a graphics upgrade from the base game…We have employed methods that we did not implement in the base game. You can literally bring your camera up to a wall now and the textures would be crisp – at least in most cases.
 
80, 85, probably even 90 per cent of the assets – in terms of environment that you find in this game – are brand new. You can just look at the market stalls right now: you would never see the same market stalls in the base game. For the longest time we were like, 'I want this, I want that,' and finally we got this chance – we got this room to incorporate other people. We have probably 20 times the amount of vegetables we used to!
 
We just wanted to show that we can actually push it to the limit this time."
Wild Hunt struggled a bit when it originally launched in May of last year, but a lot of that was due to the previously PC-centric studio having to optimize the game alongside a console release simultaneously. Sure, Assassin's of Kings came out for Xbox 360, but not until about a year after its initial launch on PC. 
 
De Gracia admits that mistakes were made along the way to Wild Hunt's release and that in many ways, Blood and Wine was built from scratch as a result of lessons learned.
 
"Before, each and every prop had its own texture; this might require another draw-call or so. It impacts performance. But this time around we know we're going to group these things together so you have them representing same texture now, so we're loading less but maximising the quality at the same time." 

The graphical optimizations will only apply to Blood and Wine, however and not the base game. With Blood and Wine being its own separate thing, it would be quite difficult (and time consuming) to go back and re-optimize everything in the whole game. Considering this is the last DLC and that most of the studio has already moved on to Cyberpunk 2077, I wouldn't expect a complete optimization overhaul to happen any time soon. 

Source: [Eurogamer]