VideoCardz compiled everything they know about AMD's Radeon M400 with references in a new driver and comes to the conclusion that most of AMD's upcoming Radeon M400 laptop GPUs will consist of rebrands.
The high-end seems to be the exception to this, the Radeon R9 M480/M485 and M490/M495 series are expected to be based on the upcoming Polaris GPU:
You might think that so many rebrands are a bad news, but the lack of high performance chips in drivers is actually a good sign. It means that Amethyst / Tonga based products will be replaced with something faster, quite possibly Polaris 11. It is expected that Polaris GPUs will be integrated into Radeon R9 M480/M485 and M490/M495 series.