It's a negative that it's not upstreamable. I wouldn't go so far as to say it's bad, but it's less than good. That means you'll continue to maintain a separate kernel module that's rebuilt for each kernel.
It would need to be modified to match the kernel's coding standards and whatnot. Part of what makes linux such a strong thing is that you're just not allowed to do certain things in the kernel. They won't include ZFS in the kernel because it's got its own entire vfs -- linux filesystems are only permitted to use linux's vfs, and if you need vfs changes to make it work, you modify the 'one true' vfs. They didn't include the original AMD Radeon driver because it had its own hardware abstraction layer; you're supposed to do that in user space or not at all. (the Radeon driver was changed to remove the abstraction layer, and it was later merged into the kernel)
It's not immediately clear to me how much work it will take to get the driver into the kernel. Hopefully it won't be a lot of work, but it's possible that it would require basically rewriting it from scratch. It's at least written almost entirely in C, so that's a good start.
Regardless, this is tremendously good news.
