I've noticed that sys-kernel/gentoo-sources is missing the BFQ patches, and that the BFQ homepage has no patches for 3.18 (yet). Anyway I tried the patches for kernel 3.17 and they still apply cleanly, so I think you could add them back.
It does not compile properly, sorry for the bugspam...
The compilation problem was a dupe of bug #527534, after massaging the second patch in the series it compiles fine, reopening...
For the future, I'd like to hear from upstream on the validity of patches for a different kernel version before blindly adding them. I will always wait on properly versioned patches from upstream to be on the safe side. That being said, they have released 3.18 patches for BFQ and I am in the process of releasing them now.