"[On Forever's lighting changes:] I think they were made here first, is a better clarification. I think they're planning on eventually doing some of these same things in the Retail game as well. So it's not like it's a Forever-only feature, like better water, better lighting, those things are coming for retail as well. I don't know when, but I know they're talking about doing it," via IGN.
Honestly, having put a solid 50 hours into the beta, I'm really glad to hear this. While I might hum and haw about some of Blizzard's design choices, the graphical overhaul of Forever is truly impressive. Part of that is in the hand-crafted nature of it; Blizzard has had to go in and, one-by-one, adjust each zone's lightning and color palette.
The results are downright gorgeous. Durotar is by far my favorite, with the saturated cool shadows contrasting the bright orange, Nordrassil visible in the distance at the top of Mt. Hyjal, and the lovely sunsets cast over everything. Other zones are pretty, too—the godrays that poke through the canopy of Ashenvale, for instance.
In the interview linked above, Zierhut goes into this in some more detail: "In our minds 20 years later, we remember what WoW was like in 2004 as just a little bit shinier and better than it actually was. So there's this vision of, let's give people Azeroth as they remember it, not as it actually was … So let's make it actually look as cool as our memories tell us it looked."
This new lighting tech, combined with retail's art direction, should produce something really special. But it also makes sense that it hasn't been done yet; it's a far, far bigger project. The classic foundation that Forever's built on has a few dozen zones to handle, whereas retail has zones from over twenty years of expansion packs.
Actually, we can see exactly how many more zones thanks to WoWHead—WoW Classic has around 114 zones (including unused zones, raids, battlegrounds, and so on). The list of current zones up to Midnight? 1272. Over ten times as many. It's an unimaginable amount of work to go through and bring them all up to standard.
But is there a reason why future retail zones can't use this tech, while it goes unused in other zones—or is added retroactively? From a technical standpoint, most likely, but I can imagine that's a solvable problem for the retail team. And judging by Forever, the world will be well worth the effort.
