A while back there was a comment that the reason we didn't see the Gladiator-style feats in MP was because they were being developed for another book. I'm guessing that they were designed for DP, since we haven't seen anything about them yet for AP.
I don't think that the domain powers (ie, at-will feats) are overly powerful. I do think that some care will need to be taken with regards to assigning powers to domains, otherwise you're stuck with all the (for example) clerics of a deity using the same power. Sure, they'll have a bunch of options with that power, but it will always be that power. Although with two at-wills, perhaps it won't be too bad.
I'm sure the player of the cleric of Kord in our group is both excited and disappointed.
The divinity feats continue to be a mixed bag. Creation Secret is rediculously awesome.
As for rampant speculation: the planes references suggest Planescape. However, what suggests it more is the comment that it will be useful for most campaigns. Hey, guess what the main headquarters in DMG2 is supposed to be? Sigil. I'd be highly surprised at this point if it were anything other than Planescape.