Please remember that until something is officially announced, these are all rumors, and are to be treated as such.
Horus Heresy book, first in a series, based around Isstvan III. To be announced at Games Day (...though not sure whether that's UK or USA).
A little birdy in the FW production line has said that they had a meeting and that there would be 2-3 waves of (big exciting things) that would happen towards the end of the year in spite of the Hobbit release. Of course they didnt tell the workers what they were...
I can be more specific ....
There are three Heresy books coming .... the first one later this year.
...and yes you are quite right there are some big and exciting things coming with them.
via Larry Vela at Bols
This is in reference to Forgeworld, and is said to occur after the next IA book which has already been announced. There was talk for years that within the company there were ardent opponents of the Heresy ever making an appearance on the tabletop as it might fragment the playerbase. So something fundamental must have changed if Forgeworld got the greenlight.