Nope, no inside info, maybe my misunderstanding. I guess I didn't RTFM :)
I also haven't heard of anyone using it but then again I don't read these forums all the time, looking for USB3 comments.
So it looks like I'm wrong but if USB 3.0 is supported, I'd like to know if anyone has gotten it to work just for my own knowledge.
Personally, on a test machine I had FreeNAS on it had USB3. I enabled it and used a USB3 thumbdrive on the USB3 card. It booted and was less than 5 seconds faster. The only reason I can think that someone would intentionally use USB3 regularly is:
1. For backups to a USB3 drive
2. If they were dumb enough to do a zpool over a bunch of USB3 drives.
If you do #1 then your zpool isn't likely to be very big. ZFS really shines for huge zpools, so I'm thinking there's relatively few people that will fit this option.
If you are option #2 I don't really want to know they're doing that. It's just stupid for so many reasons.
So yeah, I think that there are VERY few users that actually use USB3 because it will provide a benefit. I think most people that want USB3 think that it'll make the system so much faster because "their boot drive will be less restricted". The reality is that their argument is completely incorrect.
I do have an Intel External SSD that is USB3. I am now kind of curious to see what kind of performance I could get from it.