BFQ has been in development for several years as the Budget Fair Queueing I/O scheduler. BFQ aims to provide low latency for interactive applications and soft real-time applications, higher speed for code development tasks, high throughput, and strong fairness/bandwidth/delay guarantees.
BFQ has been used for a while now by some different Linux distributions that have opted to carry the patches. It's seen a lot of work over the years while finally for Linux 4.12 it looks to be mainlined.
The BFQ scheduler has been queued in the Linux-Block For-Next tree meaning it should then be sent in for the upcoming Linux 4.12 merge window.
Those interested in more BFQ details can find them via this commit that includes documentation on the new I/O scheduler or via the project site. BFQ won't be the default I/O scheduler but we'll surely be testing it out again as soon as it hits mainline to compare against CFQ, Noop, and Deadline.