It is a good bet that a significant amount of code in the kernel is
entirely unused. Even so, that code must still be maintained and shipped,
posing an ongoing cost to the development community. What should be done
with code that is unmaintained and, possibly, unused? Answering that
question requires understanding which users still exist, if any, and taking
a hard look at what the future support requirements for that code will be.
The kernel community has recently discussed this problem in the context of
filesystems, and the Reiserfs filesystem in particular, with a focus on the approaching 2038 deadline.

Source: LWN.net – [$] When and why to deprecate filesystems