I sent an e-mail to CDPR, and they told me that they have plans to roll out The Witcher 3 on Linux, but they don't have the exact date yet. It might be after the Windows release date.
I does not bother me to have a Linux version released later than the windows version, what matters is the fact that they are going to do a Linux version.
I won't be surprised if they do... I'm not so skeptical after playing BioShock Infinite, but The Witcher 3 seems much more demanding and I wonder if eON can handle it?