I've actually been contemplating this for quite some time. Ever since I learned that the druid will not be included in the new PHB, I've been concocting a recipe for what I think a druid should be from the scraps of information I can collect on the 4E game.
It's not an easy task; every two or three weeks I learn of some new innovation or strange rule that is getting incorporated into the new edition, and it forces me to rewrite large portions of my concept. But here are my assumptions, ideas, and notes on the topic.
(And for the record: I hereby give Wizards of the Coast or anyone else who is interested, my complete and full permission to use any of the material in this post. The sooner we get an awesome druid in 4E, the better.)
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Mechanics: the druid should be more durable than a wizard, but not as hardy as a fighter. So druids should probably have the same stats as a cleric (attack bonus, save throws, hit dice...assuming these things still exist in 4E), but that is where the similarity should end. Everything else about the druid should be completely different from the cleric: skills, talent trees, equipment, power source, spell selection, feats, class abilities, and so on.
So start with the cleric. Strip away its skill list (if 4E even has them) and drop all of its class abilities. Replace them with special "druid" abilities, like these:
Per Round: druid fire (ala Terry Brooks' "Shannara" novels). Sort of an at-will burning hands spell effect, that gets stronger as the druid's level increases. Deals slashing or fire damage, whichever is most effective.
Per Encounter: wild shape? summon nature's ally?
Per Day: call of life (restore one animal companion to full health)
Sadly, each of these abilities would have to be created from scratch. Apart from the ranger, there will be little "druid-esque" abilities to glean from other classes, I am afraid. So lots of work here, and balancing would be a chore, but very rewarding.
Talent Trees: I am assuming that the talent trees will work in the same way as combat styles do in Book of Nine Swords. There will need to be at least three talent trees to completely flesh out the druid: one that focuses on summoning and controlling animals (the "caller druid"), one that focuses on shapeshifting (the "shifter druid"), and one that focuses on magic (the "caster druid.")
Some talent trees from other classes could be used for the druid (best candidate so far is the ranger, who probably has some martial combat talent trees related to wilderness fighting), but the majority of them would have to be created from scratch. And I suck at writing strikes, maneuvers, and stances. Perhaps the penguin herder could help us out in this department?
Spells: I am assuming that a druid is neither a divine spellcaster nor an arcane spellcaster; the druid uses a new and different power source altogether called "Gaia." In my interpretation, "gaia" is the essence of life that is interwoven into the earth itself, a resonance that connects all living creatures. The druid taps into that resonance energy and manipulates it to enhance life, summon life, or sever the life connection altogether. Non-living creatures, such as undead or constructs, would be less affected by Gaian magic, while animals, fey, and plants would be most affected.
Some Gaian spells could have foci and material components, such as a quarterstaff made from unpolished wood or a wand made from a willow twig. Others could require the caster to be outdoors or in contact with earth or unworked stone. Or not. (shrug)
It would be possible to build a suitable list of Gaian spells from the Arcane and Divine lists, I suppose...we would have to rewrite them a little for flavor, but the majority of them would be there. A few old favorites would have to be written from scratch, however: shilleleigh, goodberry, and fire seeds, for example.
Equipment: I know a lot of people complained about the "no metal" restrictions that druids had in earlier editions, but I sort of liked them. I think druids should be restricted to organic equipment only...no metal or worked stone. Much of the flavor of a class comes from its weaknesses, not its strengths.
A druid who uses a metallic weapon or wears metal armor temporarily breaks the connection to Gaia, and loses all class abilities until the connection can be restored. This could be handled with atonement, or a special sunrise ritual, or a sacrifice of the druid's own blood or hair, etc., depending on the druid's alignment.
Assuming there is a such thing as "alignment" in 4E.
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That's all I got so far. It is woefully incomplete. I have a Word document here with this info in it, and I add stuff to it whenever I get the time and inspiration...so any ideas, input, or feedback would be appreciated. And like I said before: feel free to copy, distribute, modify, use, or disregard anything in this post, in whole or in part.