We're already seeing some significant changes to the way gear works in Wrath of the Lich King. However, in a thread on the official forums about the ever-increasing character level cap, Bornakk steps in to set at least a few minds at ease regarding the way gear will scale. He says the developers don't plan on overhauling gear in Wrath quite the same way they had when TBC came out. So, while the items will be more powerful, we shouldn't see the same disparity between WotLK items and pre-WotLK items that we did for BC gear and pre-BC gear. It won't be like you'll pick up a green from a level 71 quest that replaces your S4 gear.
But there's a bunch of stat changes in WotLK that've already been revealed. Does this mean the spellpower changes will go back through all of the BC gear, or is it just that the item level is going to remain a steady scale? Or will unified spellpower only be available in Northrend? Eh, we're only in Alpha right now. Just the notion that Blizzard is aware and considering this issue is enough for now, and I guess we can wait and see how the drops will look.