There is only mention of Solaris 11.next (see graphic below) which is mentioned for cloud deployment and integration enhancements.
Back in 2014, Oracle had indicated in its roadmap that Solaris 12 would appear in 2017 and would be developed over the next two years.
Oracle became the owner of Solaris, an operating system developed by Sun Microsystems, when it acquired the latter company in 2010.
Oracle has not been known to be a good custodian of the open source assets it acquired as part of the sale, hiving off OpenOffice.org to the Apache Foundation.
Both OpenOffice.org and MySQL were forked as LibreOffice and MariaDB respectively and now enjoy a major share of the market which their parent applications once did.
With Linux having cannibalised a great deal of the Solaris market, one can understand Oracle's logic in abandoning plans for Solaris 12.
According to the Oracle support policy, there is premier support for Solaris 11 until November 2013 and extended support until November 2034.