Question about Psykers in 6th Edition

Looking back and forth between the forums, it seems that Inquisitors upgraded as Psykers is flavor of the month. With the new Prescience psychic power it allows the squad to re-roll to hit, making squads have twin-linked psycannons and storm-bolters .

However, my question is: is the ability to get the prescience psychic power only limited to Inquisitors and Librarians? Technically speaking you could upgrade your GM to Psyker level 2, so can he choose to have new powers from the rule book? And do other Psykers within the codex (with mastery level 1 - i.e. techmarine) gain the option as well?

If the techmarine can use the prescience psychic power, wouldn't he be best suited for SS or Purifiers? I don't like the load out of a xenos inquisitor.

Thanks for any responses

unfortunaly errata says only Libby and Inquisitors can swap their powers