Sorry i guess i don't know how to google then. This was stated pretty early on. But it is an official source. I guess that means the build up of "choosing your abilities carefully" was just a lie then. Since locking in gives you the stat boost you want and the new class still allows you to customize and fiddle around.

Locking in still means in order to have options you have to spend the time to level up the copy. Even if quicker, it's not just being able to change at will. What will end up happening, is you'll want to level up several builds, one for PVP, one for raids, one for solo PVE etc. This along with leveling all your gear, different gear will better suit different focus builds, and the activities to acquire the best gear in the first place is going to give Destiny's end game a lot of time to finish. The newest IGN first video shows an exotic titan helmet that gives you one of the fist of havocs upgrade options. Thus allowing you to choose a different upgrade and have both. That's the type of interactions between gear and build you're going to have. Different gear will work better with different builds. And you're going to want to lock in those different builds to maximize their potential.

I see your point. But there only appears to be one extra slot. So we can only lock in 1 sub class. Meaning at most we'd have 3 seperate builds.

I'm sure you can store extras in the vault

Maybe. But there really isn't a point in locking in twice since it only boosts one of the stats.

It only boosts one Stat while that focus is equipped. So if you want multiple builds to be at their full potential, you'll have to lock in each build

I thought it only boosted the main stat of the class?

It's like the other passive stat boosts in your focus. When you swap the focus you lose all the bonuses you got from that focus. It's not a permanent modifier to your character.