I wonder if this concept would work...

For character creation, you choose any 2 class powers, and 1 power source, and your at-will/encounter/utility/daily can come from any list, as long as you have any pre-requisites. Now you have completely customizable characters.

So, for instance, I could build a duelist by choosing TWF from Ranger, Dagger/Shuriken bonuses from Rogue, and Martial as a power source? Interesting idea. You'd have to figure out Defenses (Maybe +1 to any 2, and +1/+2 for Defenders) and class skills, but it would be doable.

Perhaps it would be better to do it based on 'Roles'

I.E. I'm building a striker, okay you gain the HP of the strikes (12+con 5 a level) you gain +1 to Ref and +1 to either other, you gain cloth, leather and chain armor prof., simple weapon etc. then you can pick powers and abilities from other striker classes?

I like the idea but there is more than just the powers to deal with.

I like the idea alot too. Perhaps not being "classless", but a great way to whip up a new kind of class.

You should probably have more than two class features, and at least two categories of class features, since many of them are not balanced with each other. For example, the Warlock's Eldritch Blast class 'feature' is pointless under this system, the Ranger's archery talent is weak, and the Fighter's Combat Challenge ability is strong.

That's a better idea, but I don't see where strikers have Chain Armor proficiency. Rogues and Warlocks have leather, Rangers add Hide. Remember, too, that Chain is now considered Heavy Armor.

How is it weak?

Ok, let's take the Eldritch blast feature as an example. It's considered a basic ranged attack, and lets you use powers that can be used with that. So any ranger ability that requires a ranged weapon (Nimble Strike, Fox's Cunning) works fine with it. Hell, so would Magic Missile and those abilities.

My mistake on the Chain, but yeah, the point still stands, you pick a role and get the basic 'stats' of the role, then can pick your class features and powers.

As for the balancing of class features, that's up to the GM to ensure that the made up class doesn't overpower everyone else.

First, you're wrong. Being a ranged basic attack doesn't make it a ranged weapon. You need an actual weapon for those.
Second, the class 'feature' just restricts your choices of at-will powers; it doesn't give you that power in addition to your other at-will choices. That makes it useless when you can pick any at-will powers you want.

Truly, Wippit, in 4E the Devil is in the details.

Specific trumps general; the keywords in each power trump any general combat rule. Take a look at the Ranger At Will power Twin Strike. It states that you must be using two melee weapons or a ranged weapon to use it. Eldritch Blast is NOT a ranged weapon; it's an At Will power that can be used to make a Ranged Basic Attack.

Now, there are other powers which allow an ally to make a basic attack. (I'll have to check for an example, but check the power lists for Leader classes.) In those cases, certain At Will powers, like Magic Missile and Eldritch Blast, can be used instead of an actual weapon.