Okay, so I had this idea that came up and thought I would start a discussion to get everyone's thought about it, including Marco.
Here's the idea. What if one item, say an unique item, could unlock a whole new skill tree. That's a little hard to explain, so let me make up an example to explain the concept. Let's say you have the following unique wand.
The Elder Wand
Grim Wand (Sacred)
One-Hand Damage: 77 to 88
Durability: 108
(Necromancer Only)
Required Dexterity: 172
Required Level: 100
Adds Dexterity Damage Bonus: (25/256 per Dexterity)%
Unlocks Wand Wielding Skills
some stats
Socketed (2)
Now, when you equip this wand, it would append a brand new page to your skill tree, with a new set of skills to put points in. The said page and skills wouldn't be displayed unless you have this item. Removing the item would remove all points you allocated into these skills. In other words, the item is the build. This concept already kind of exist as it is, with unique/set/runeword items that grant a set of oskills allowing the player to create decent new builds, but this would bring this concept on a whole new level.