How about "angel"? Or maybe "deva"? A quick flip through the dictionary shows either of those as more appropriate than "archon", which means "game played with multiple monsters on a modified chess board".
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That says 'Angel' to me, honestly. The previous Archon is an artificial seperation created so we'd have a celestial of every individual Good alignment on the wheel. Since they're going away from that aspect anyways, why keep it? Any specific 'Old' style archon that's sufficiently neat enough to keep around can go under 'Angel' as a broad specification of 'Good' servitor race. Just as Devils are no longer 'Those LE Outsiders', there's no longer a reason to keep Archons as 'Those LG Outsiders' besides 'It's always been like that'.
The reason is the same reason they're keeping the demon/devil division. We have different flavors of good that are big enough to contain several different critters in each. It could also be because, as posited, "Angels" may no longer even be just a flavor of good, they may instead be generic god-lackeys.
I'd have no real problem with calling the crusading spirits "Angels." But, then, what do you call the other ones? Say, the protective spirits?
Think of the various fluff roles of good outsiders, and about what roles might be needed and useful for the game. Hitting the previous editions, we have creatures like Eladrin. They're becoming fey and they fit that mold better, so they'll be happy there. We have Animal Lords, and, again, they'll probably work better as fey. We have Guardinals -- ostensibly guardian spirits. We have Archons -- ostensibly warrior-celestials. And we have Angels, which are also known as Devas, which are generally described as messengers of the gods and/or protective spirits.
For the game, we could use fey spirits (Eladin, being done). We could use servants of the various deities (possibly, as speculated above, Angels of various good and evil things). We could also use exemplars of Good that kick evil's butt (????) and and exemplars of Good that help out the innocent (????). The reason for this is the same reason we need exemplars of Evil that kick butt (Demons) and that tempt the innocent (Devils).
Now, in a sort of ideal world, we'd keep the cool name for the evil butt-kickers (Archons), and we'd use the most evocative and culturally accurate name for the spiritual wardens and announcers (Angels). You could draw some parallels, if you wanted. Angels and Devils are controllers and leaders, both fighting over the innocent, but ultimately leaving the choice up to them. Archons and Demons are defenders and strikers, both killing those on the other side, ultimately concerned with life and limb. You could still have the various god-servants, and if you wanted a category for them all, you could either make one up (Godspawn?) or even take one of the discarded names from previous editions if you love it (Devas?).
But they're not going with that. Maybe they have something better in mind. It's said in R&C that they're doing something dramatic with celestials and the Forces of Good, too, because they were generally boring in other editions. I'd agree with this, and I'd love to see some forces of good I can really sink my teeth into. The above scheme is pretty good for that (Archons fight 'morally ambiguous' PC's, and ally with party clerics and paladins when facing evil; angels need help defending people and can always offer blessings to PCs who they must recruit). We don't know what scheme they have cooking up, maybe it'll be even better.
All I know for sure is that the word 'Archon,' which was in a valid and interesting place as of 3e, that could, as far as I can see, still fill that place in 4e and be even MORE valid and interesting, was instead given up. The reason? Because dog heads are only for furries. It was instead placed on another random creature The reason? Because it's too cool of a word not to use.
Angels instead may be "generic divine servants." And Archons, we can see, are "manmade elemental people." You've lost the strongest associations of the names. And what have you gained? Jack, as far as I can see. And why have you gained it? Because your imagination failed to speculate on new words, and because your imagination failed to consider that Archons could mean something much stronger to current players than "those dog-headed celestials."
My major, major issue with this is that their stated reasons for these moves are remarkably boneheaded and shortsighted, giving us nothing truly great (the monsters are cool regardless of what you call them, and calling them "Archons" doesn't make much sense given what "Archon" means) in exchange for ruining something that was pretty good to begin with (even if people had issues with Anubis-style paladin-celestials, the idea of a caste of warrior-divine-things is a strong monster family category, at least as strong as Demons being destructive-evil-things).
...there's also this:
Says who? What does your game actually need any caste of creature that crusades for good for?
Is the game actually served by winged green-skinned baldos made out of fluff and sunshine who always fight for what's right more than Bahamut's Angels of Law, beings forged of law and cold iron who, while delivering your group from the talons of the enemy, would gladly slay you for your sins against the universal Law in the blink of an eye were it not for Bahamut's commands that they not. And the whole time they wing you away from the burning palisades, you can see the cold hatred burning in their iron eyes as they look at you...
'Cuz, you know, those angels are exactly as helpful as Solars ever were in adventures, and then you can turn around and cut them to bits when they're Bane's Angels of Law.
Which seems to miss the point that it's not the individual celestials that I'm that concerned about. It's the potency of the word "Archon" to mean "Ass-kicking Heavenly Spirit of Goodness" in the game, and that this is a stronger association than the word "Archon" meaning "Frankenstein Elemental."
As the post demonstrates, ass-kicking spirits of goodness can be a fun game element, especially since 4e will probably have more than a few "morally ambiguous" members, and because alignment is less important, it will probably have significantly less truly Good members, giving Celestials of all stripes more imparative to kick some PC's around.
This is all good stuff. But the argument is a semantic one. What should we call ass-kicking spirits of goodness? Previous editions called them "archons." Why can't 4e? Apparently because of one dog-headed angel and a whole lot of imagination failure.