However, if you check in the development thread, there is a temproot method out that works for most "root" applications.
I wouldn't call it full root tho, simply because the system is still write-protected, so you can't make any permanent changes. So you can use xposed for the most part, but you have to do a soft reboot to make it kick in, and you have to reinstall the framework and reactivate modules after a reboot.
Still, it's incredible that we have that much being so early in the release of the device. I'm hoping that the firewater S-off method used for the VZW M7 will be made to work with the M8...then we can do whatever we want.