http://www.3plusplus.net/2013/12/feast-of-blades-will-be-enacting-restrictions-and-bans/#more-86921.) The Grimoire of True Names from Codex: Daemons is banned
As of right now, this is the only true banning. We feel there is too much potential for abuse, and disagree with the effect it has on the army and the game.
2.) A few units will receive 0-1 status
For those of you who weren't around when 0-1 was a thing in codecies, means that a maximum of 1 of that unit may be taken per army. These are all units whose mass inclusion limits the potential lists in the game, and will thus be restricted. (As none of them are a problem on their own.) Rest assured that this will be a very short list, we are not interested in creating very restricted armies.
3.) Supplemental Codecies will no longer be able to ally to their base codex
There will be no more self-allying, no more cherry picking the best parts of a supplement while paying none of the costs, and no more force-org bloat from doing so.
4.) Dataslates will take an ally slot
Taking units from many, many different books and ignoring the force organization chart is too much. This change will make dataslates an interesting addition to the game, without allowing for truly bizzare armies.
5.) The number of psychic mastery levels in an army will be limited
This change will eliminate a great many power combos from the game, and will stop a player from making a lot of lucky rolls on the psychic power tables to effectively win the game before it begins.
6.) Strength D is out, Lords of Battle are in
We feel the the Lords of Battle are not overpowered on their own, the fact that they give the opponent some advantages (bonus to seize, and especially victory points) balances out their fearsome firepower and powerful endurance. Strength D, however, is too powerful. This is well-known by every apoc player (and I am one of them), and has been the case for the past two editions. (Yes, it was even overpowered back in 5th, and it was much worse then.) There is some debate still going on, but it looks like S:D will become S:10, ordinance, ignores cover. That still makes it very powerful, but more in line with the price paid for the superheavy as well as it's other weapon options. In addition, superheavies will have to start on the table.
7.) Super-forts are gone, or at least downsized
No AV15, it will be AV14 instead. Every individual fortification from Stronghold Assault is allowed, but the “network” choices are simply too big and unwieldy to allow for tournament play. (As a consolation, they're pretty terrible, so I think it's OK.)
8.) Dedicated transport flyers will be limited
Flyers are not the be-all end-all of this edition, but all-flyer and mostly-flyer armies change the meta in uncomfortable ways and are notoriously unfun to play against.