I've heard from two sources within GW that they have seen work in progress CAD thingamies for Dark Elf plastics, of which Witch Elves were named specifically. Another kit was mentioned as being Black Guard or Executioners. There was also another plastic kit he didn't recognise and some plastic characters. I'm embarassed to admit I can't find the original email to check exactly what he said. I think there may have been some large plastic critter as well.
EDIT: The other source just mentioned Witch Elf CADs which he wasn't too impressed with.
I've had this corroborated by another rumourmonger who said it fits in with what he heard of Dark Elves coming in 2013 and CAD images meaning they are usually 18-24 months or so away from production.
As always, until pictures are leaked or GW sends out an email treat it as rumour not fact.
Harry hints at some future Dark Elf releases as well:
Originally Posted by Harry
There are ... currently no rumours for Dark Elves.
That doesn't mean there is not a bunch of stuff in the pipe line for them.
Now there are rumours for Dark Elves.
However, like Eldargal, he says they aren't to be expected soon:
Originally Posted by Harry
I am a good deal less vague with stuff that is 'next' ... see the Vampire counts rumours from about 3 months out I started to to give details and I imagine when we are 3 months away from Dwarves or Dark Elves I will be less vague about them .... but that is not yet.
I want to come back as an octopus in the odd chance I will be able to attach myself to a young womans b3wb, alas I will more likely be served with some rice and a nice sauce.