We still don't have class blogs up yet (not sure if that'll be midnight PST or when) but apparently some details about Demonology were revealed in the Darkmoon Faire chat at Blizzcon.
First off, yes Metamorphosis is being stolen (or arguably stolen back) by Demon Hunters.
Also, all Warlocks will use Soul Shards, which frankly I'm not too happy about, as I liked the way that all three specs got their own secondary resource. Still, they'll hopefully work in a more interesting way than the old Soulburn mechanic.
Demo is going to be about building up swarms of demons to send at one's foes. They've rebuilt the spec from the ground up (kind of inevitable post-Meta,) but we know that Shadow Bolt and Hand of Gul'dan will still be in the arsenal. HoG might be a Soul Shard (or whatever resource) spender, while Shadow Bolt will build it.
Demo will have lots of demon summons - they're really focusing on the summoning of multiple demons. Included here are the Felstalkers (the kind of sleek Felhounds we've seen in Tanaan Jungle,) and apparently you'll sometimes get Felstalkers with Imps riding them, which is pretty fantastic.
There was talk of summoning a Dreadlord, but not as a permanent pet (to be fair, Demo already has a unique pet in the Felguard/Wrathguard.)
More details presumably tomorrow.