XFS: the filesystem of the future?

Here's some advice. Shrinking a filesystem, any filesystem, is generally very problematic and often not supported because it is a very complicated operation as detailed elsewhere in the comments. My policy is to use LVM to size the filesystem for your immediate needs and a small amount of breathing room and extend as necessary. Good, modern filesystems can safely extend while mounted. With that policy you would never have the situation you describe, you would either add space where it is needed or there just physically isn't enough space and you need to buy more, those are the only options and both are easy to support.