EKWB explains that due to the similarities between the older Radeon HD 7970 and the new Radeon R9-280X, and since there was no official reference design for the PCB, most of the AIB partners have decided to either re-use the older reference design (AMD 109-C38637) or proprietary designs, including Asus' DirectCUII boards. EKWB has also renamed the EK-FC7970 Matrix to the EK-FX R9-280X Matrix, just to prevent confusion.
Because of this, EKWB has announced that its older EK-FC7970 CSQ series of water blocks, or other EKWB EK-FC7970 series of water blocks, will work on the according graphics cards. EKWB has also announced that it has added compatibility in the compatibility database to make finding a water block for your new Radeon R9-280X easier.
Lastly, EKWB also announced that it is working on a water block for the upcoming Radeon R9-290X, and that the official blocks will be available starting October 18, 2013.