The kernel patch for Solaris 10 8/11 (Update 10) have been released on OTN, the patch information is available here. This indicates that the new Solaris update is due for release quite soon. The patch metadata confirms my previous speculations regarding updated ZFS functionality that even includes the new hybrid block allocator.
One of the most interesting things is that it includes support for upcoming SPARC T4.
6946852: Solaris support for SPARC T4 platforms
As always it contains numerous bug fixes and other enhancements, follow the links bellow for previous posts about new features in this update. More information will be posted when full images of the update have been released.
The ISO images seems to have been available briefly from Oracle but have now been pulled for some reason, you can still see the links in googles cache but the full page is not available.
Solaris 10 update 10 update
Solaris 10 update 10 ZFS refresh
Solaris 10 update 10
Talks I have given
5 months ago