Yes, this is true. It is not (yet) part of the full standard, but it is
"provided as information and guidance to implementers". Details at
http://www.unicode.org/unicode/reports/tr7.html
Additionally, there is a document that shows what characters and scripts are
"in the pipeline", which includes several scripts (Linear B, Etruscan,
Gothic, Western Musical Notation, etc.) that have or are expected to be
allocated space in Plane 1. UCS-2 is history.
/cco