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There is -fno-rtti, -fno-exceptions, -Wmultiple-inheritance, -Wvirtual-inheritance, -Wnamespaces, -Wsuggest-final-types, -Wsuggest-final-methods, -Wsuggest-override, -Wtemplates, -Woverloaded-virtual, -Weffc++, -fpermissive, -fno-operator-names and probably many more. The warnings can be turned into errors, e.g. -Werror=namespaces.

No two development groups agree on the desired features, so it would have to be a custom compiler plugin.

You could start with a Perl script that looks at the output of “clang++ -Xclang -ast-dump” and verifies that only permitted AST nodes are present in files that are part of the project sources.

For sure no two groups want the same subset but is there no "standard way" to opt in / out in the ecosystem? It's strange that there are large orgs like Google enforcing style guidelines but manual code reviews are required to enforce it. (or may be my understanding of that's enforced is wrong)

Yes, via static analysis tools it is possible.

As usual with additional tooling, there must exist some willingness to adopt them.