It would be a smart move.
Irex could save money on development, because people would develop (hopefully) the software for free
The device would ship with different versions of the software, so every people would find their needs.
I think that the hardware itself is the most important, not the software in this case. Because the hardware is revolutionary (e-paper technology), but the software is (Linux) is not new. So it would not hurt the device if they would make the software open source.