Auto answer:
As I cannot tell if someone isSysop, I used one of the specific Sysop
action as a filter (move, or delete). Or I use isallowed("userrights")
to check if visitor is a Bureaucrat.
And it works fine :-) to restrict edit to one single namespace
if ( !(1 == $this->mNamespace) && !$wgUser->isAllowed('userrights')
) {
wfProfileOut( $fname );
return false;
}
François