UML22 — Profile Semantics, pag 723

"A reference metamodel typically consists of metaclasses that are either
imported or locally owned. All metaclasses that
are extended by a profile have to be members of the same reference
metamodel. A tool can make use of the information
about which metaclasses are extended in different ways, for example to
filter or hide elements when a profile is applied, ..."

The specification must be explicit about the mechanism used to hide/filter
reference metamodel elements. The SysML Partners are trying to do exactly
this with SysML but it's not clear from the above paragraph or any other
part of the Profiles section how to do it.

see above