You can't use lx-branded zones in Solaris anymore, but SmartOS has revived and continued the project, and OmniOS has started porting the bits into their distribution, too.
After Oracle bought Sun. It was never a part of Solaris 11. I don't know if it's still part of Solaris 10 or not, but even if it is, it's only barely usable.
But it's alive and well (and awesome) in SmartOS, with active work going on to merge it into OmniOS, and eventually will be upstreamed to illumos-gate.