We've been discussing the mechanical aspect of classes, as that is what makes creating new mechanics necessary. Concepts are a different, but related discussion which I avoided for the purpose of keeping the discussion to a reasonable size, especially since concepts are so much broader a topic than mechanics, and I've already written more than enough on the topic in blogs:
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The amount of work to make a current class into something comparable to the classes I've composed would be be about as much work as building a class from scratch, with maybe some space saved on utilities.
The Glamor Blade daily power does indeed get the most basic gist of the class, like how a wizard's conjuration does a shaman. Now build a class around the concept utilizing that instead of all the teleportation and other arcane-feeling stuff that Swordmages do, remove their weapon type restrictions, add encounter and daily powers that do interesting things with their proximity to their conjuration, so on and so forth. It'll end up resembling a swordmage about as much as a warden does, and open up space for a variety of "warrior with a magical partner" concepts.
Wizards and druids and invokers so forth can be built to be front-line focused, but in the same way a slayer can be an archer - they're still not a ranger. Building a class around near-range options, with the ability to convert most or all of their abilities into close or short-range attacks creates a very different feel. Controllers are perhaps the easiest to modify into random things, simply because they're defined by their powers rather than their class, but you can get more variation on a concept if you work with a narrower field than "everything" and create that can work in interesting ways within that concept.
To clarify, the striker concept is that they make attacks from an ally's square, but they're the one making the attack, allowing them to utilize class-specific abilities rather than modifying their ally's abilities - attacking from an enemy's square is also a conceptual possibility. Imagine a character who can gesture at an ally (or an enemy) to momentary conjure a demonic visage in their flesh, which then stretches out to chomp into the actual target. It's a class that would rely heavily on controller or leader abilities to position things so that they can reach exactly the target they want, allowing them to attack around corners and from behind the enemy's cover. I would personally find it very satisfying to stab an evil cultist through the heart through his own tied-down sacrifice.
Moreover, adding new mechanics to the game gives people more to apply their imagination to. There is some overlap, but such overlap is usually going to be in limited-use abilities rather than constant use ones, like that Swordmage daily power above, or a wizard's summons compared to an animal companion. Not everyone would care for such archetypes, but not everyone cares for the fighter, rogue, cleric, or wizard.
Certainly, I won't claim that new classes need to be added -constantly- or -now-. Say four classes per year, and only so long as they had actual new ideas to flesh out rather than doing it for the sake of doing it, would be great to me.