There is nothing stopping Linux from mainlining ZFS at the source level apart from kernel developers reluctance to give into "layering violations." Somebody can correct me if I'm wrong.
To wit: I am not sure if linking and terms of binary distribution matter after sources have merged for open source projects. If you have the source code and have right to modify, merge and distribute it, arguing about static or dynamic linking and binary distribution is like arguing about the color of your car door after the car has been made. It's inconsequential compared to amount of IP and resources put into the source code, and easily changed by any user (to a different architecture lets say).
Modifying has no meaning when it comes to binaries. But it's core to copyleft and open source. You would only care about binary licensing if you were a closed source product, and had to have ultimate control. If somebody had complete copyright over a ZFS binary, they could say how it can be used or not. The way an EULA would restrict you. Since no such copyright holder or binary exists for ZFS, and only source does, I don't think most people would stop collaboration in source code once the licenses are compatible.
Linking exceptions are for those who do own all of the copyrights and want to distribute along side open source software, and having a distinction otherwise in the open source world adds to license proliferation and makes no sense. ZFS doesn't have a single copyright holder acting on it's behalf, it has lost certain privileges because of this. I'm sure Oracle would be troll about this too, but they would probably be wrong given FreeBSD and OpenZFS.
I do think the GPLv3 fails a little bit because of the same argument. But I'm no lawyer.
