Psychic powers are going to be one of the big changes starting this coming weekend with 7th edition. There are more details now coming out, about who can and cant use the Daemonology powers, Maelfic and Sanctic disciplines. It looks something like this.
Everyone but tyranids have access to the Daemonology Discipline, which is broken down into two sets of powers, Sanctic and Maelfic.
Grey Knights can use Sanctic powers but not Maelfic ones.
All other psykers can use Sanctic powers but suffer perils on any doubles whether successful or not.
Daemons can use Maelfic powers but not Sanctic.
All other pskyers can use Maelfic powers but suffer perils on any doubles whether successful or not.
Here is a link to the image if you need further clarification
http://www.dakkadakka.com/dakkaforum/posts/list/595686.page