Just a thought: 2 way synergies
i.e. (using skills from D2)
You max out, say, Ice Bolt as a sorc. Generally, you would only use this as a synergy for Blizzard. Why not make Blizzard beef up ice bolt?
Or, a new idea altogether: Combining skills. Mix ice bolt and blizzard to either have ice bolts rain from the sky, or have the ice bolt explode into an AoE blizzard on contact.
Just a couple suggestions for the new system that could make early skills useful in the long run.