Quick series of little primers and reminders:
The GT/Invitational for 40K this year use, in brief, army constructed guidelines of a single CAD and another Detachment of choice, with self-allying permitted to account for the limit.
The Narrative event (Which you can do as a full 7-game GT level event or just 4 night games in conjunction with the GT or other day activities) uses Battle-Forged Army Construction, w/ Forgeworld legal, and almost all the Lords of War legal (list forthcoming).
The Trios event's singles games uses fully open army construction, inclusive of Unbound and all Forgeworld / Lords of War, and also can be done in conjunction with either the Narrative and/or the GT.
SO ... the long and short is ... there's something for almost every preference of 40K player from the present environment as folks adjust to what they like best about 7th Edition.
FYI also - there are only a handful of spots left in the Narrative full-7-game event (Warlords track), and the GT is continuing to wane in terms of spots available.