Regardless of how good ZFS is, if it can't be shipped native on Linux nobody will care. Much. Though it is a neat file system. And I would love to see it in the Kernel.
Unfortunately it's now controlled by Oracle so you're probably lucky that you can use it without hiring an 'storage consultant' for $100k+ a year.
Your first statement is unfortunately true, ZFS won't get much adoption in Linux if it's not in the kernel.
However, your second statement is blatantly false. Much of ZFS development happens in the open in the illumos and FreeBSD communities. Joyent and Nexenta base their business on ZFS and pay people to work on the open source illumos.
Those of us with data that we want to secure will care, and will run ZFS. Maybe not on Linux but on top of FreeBSD or OpenIndiana (in my case).
Sorry, but Linux isn't the end all be all open source operating system, and is the last thing I will put into a production system where I care about my data and or stability.
I installed a openindiana ZFS system for my home just a few days ago. And I don't feel alone, now my collegues probably will also seriously consider it, because I can't stop singing it's praises.
Unfortunately it's now controlled by Oracle so you're probably lucky that you can use it without hiring an 'storage consultant' for $100k+ a year.