Currently the php plugin for IDEA 13.1.5 is Version 134.1456 (March 2014). Based on what I can tell the new features found in PHPStorm 8 are only available in IDEA 14 EAP. Seems like the new features will never be made available in IDEA 13.1.x? If this is the case maybe the question should be when will IDEA 14 come out of EAP and will the PHP Plugin then be on par with what is available in PHPStorm 8?
I would not want to "downgrade" from IDEA to PHPStorm, but it becomes a difficult waiting game, especially in cases where IDEA is in EAP and PHPStorm comes out of EAP. Maybe JetBrains could offer IDEA licensees some sort of discounted purchase of PHPStorm so that we wouldn't have to wait for new features? This way we could transition to the plugin when things are more on par between the official production PHPStorm and official production IDEA versions.