So although this is NO CONFIRMATION of anything, I had a bit of banter with Forgeworld staff on their Facebook site recently, and it seems there is a strong desire to produce Ad Mech stuff. I don't know if any design of any kind has even started yet, or whether it is just in their likely massive 'to do' pile, but there is definitely strong hints that it will happen. Whether that will be within the next three to four years? Who knows, we keep dreaming...
From what I know, they've been wanting to do ADMech stuff for a while, but don't have any plans for anything yet. If they do it, I get the feeling they want to do them as a standalone force rather than an add-on for say Mariens or Guard. Creating a whole new army would be a big challenge for FW and a step up from what they are currently doing, hence why I don't think anything formal is happening yet.
Chief Educator of the Horsemen of Derailment "People demand freedom of speech to make up for the freedom of thought, which they avoid." SOREN KIERKEGAARD
The last I saw them say on the subject was that it was on their 'wouldn't it be cool if we did this' list, if work has advanced to anything more serious than that they aren't talking about it out of the studio yet.
Ask not the EldarGal a question, for she will give you three answers, all of which are puns and terrifying to know. Back off man, I'm a feminist. Ia! Ia! Gloppal Snode!