This makes me unhappy (emphasis mine):
We give you three fire archons (at levels 12, 19, and 20) and three ice archons (at levels 16, 19, and 20). But the Elemental Chaos is vast, and fire and ice are only two of the many forms it takes. Now that we’ve (thankfully!) separated the word “elemental” in the D&D sense from the classical Greek elements of earth, fire, air, and water, there’s plenty of room for archons of your own design. (And I imagine you’ll see more archons from us, too.)
It sounds like "Want more Archons? Get ready to pay $25 in a month for our expanded Book of Archons (tm) for access to even more monster archetypes that we should have included in the Monster Manual!"
...and I'm a 4e fan...