With level 50 content coming, hybrids are becoming more and more powerful. This is a good thing, am not complaining about that one bit.
What I want to suggest (and has been mentioned a few times before) is a reward for those pure class players.
Make a talent at the end of the tree that will require ALL of your points to be in one tree at level 50. Dont make it overpowered else we will lose the incentive to create hybrid classes, just make it a boost to the root of the class. Something like:
Templar - Taunted enemy loses % defense
Warrior - Double Maelstrom time
Assassin - Double Lacerated stacks
Ranger - Double Haemorage time
Mage - Double Boiling Blood time
Prophet - Double Snow time
Got lazy there with examples, but something that is at the root of the class that will give them a bonus to compete with hybrids.