An official email has been just blasted out from Sony. Hinting there may be more beta opening coming soon.
Dear G.A.P. member,
Thanks for your recent interest in the Warhawk beta test. At the moment, we have all the beta testers we need for this phase. But don't lose hope: there may be more Warhawk beta test opportunities in the near future. Keep an eye on your inbox. We'll contact you if we have space in any further phases of the Warhawk beta test.
The PlayStation Underground