Did you notice any increased focus speed after the update? Or it's just the 10-24 which is fast, as it really feels faster that I recall the X-T1 with other lenses was.
The firmware release notes included this cryptic sentence: "In Instant AF mode, which is operated by pressing the AF-L button during manual focusing, the update will enable Phase Detection AF, providing faster focusing speeds."
I'm not sure what "faster" means in the context of manual focusing. (PDAF is faster than manual focusing? Uhhh, OK.)
Personally, I'm not aware of any difference in autofocus speed since the firmware update. On the other hand, I've been very favorably impressed with how quickly and accurately the X-T1 autofocuses all along.