We already know that Destiny will have 4 different types of damage: Kinetic (which is the basic one), Solar, Arc and Void.
Also, everyone who played the beta should have noticed that there was a 3rd empty subclass slot.
Due to the facts that
The Warlocks Voidwalker is based on Void damage
The Warlocks Sunsinger is based on Solar damage
The Hunters Gunslinger is based on Solar damage
The Hunters Bladedancer is based on Arc damage
The Titans Striker is based on Arc damage
The Titans Defender is based on Void damage
I assume that the Warlocks/Hunters/Titans 3rd subclass will be based on Arc/Void/Solar damage so regardless of what class you have chosen you can deal any damage by selecting the particular subclass.
Do you agree?