It's also worth noting that file system developers should think about their file system fifty to a hundred years out. Flash drives today often still come preformatted with FAT32, twenty two years after its release in 1996. Up until a couple years ago, my dad had an external drive formatted with FAT16--a thirty year old file system.
If ZFS lives as long as the FATs have (three decades) even at a doubling every 34 months, that means six remaining doublings before 2035. Not quite 2^64, but that's on the liberal side. Half that (doubling every 17 months) is twelve doublings, which is easily over 2^64.
And let’s not forget all the crazy (better word?) features like independence from indianness. They built the file system with an eye toward versatility.
If ZFS lives as long as the FATs have (three decades) even at a doubling every 34 months, that means six remaining doublings before 2035. Not quite 2^64, but that's on the liberal side. Half that (doubling every 17 months) is twelve doublings, which is easily over 2^64.