A few hours ago, KDE 4.6.beta1 was released. The kde4-solaris project was among the first to provide binary packages, you can get them from the kde4-solaris IPS repository. The packages were built on Solaris 11 Express, I'd expect them to be installable on OpenIndiana as well. Check [ade]'s blog for more.
Update: It looks like pkgbuild is adding the build number of the build machine into the dependencies. This blocks install on OI, as the dependency cannot be met then. We're working on a solution.