Referential transparency and opacity

I'm aware there are still semantics issues, but if they're potentially
resolvable would it be possible to support both referentially transparent
and referentially opaque statements by using a different syntax for each?
So, I guess, something like:

    Referentially transparent statement:
    << S R O >>

    Referentially opaque statement:
    <<" S R O ">>

With one usage rule:

    Transparent statements can only be nested in transparent statements.

The rule means that once the <<" ">> delimiters are used everything inside,
no matter how deeply nested, is also referentially opaque, which keeps
things composable.

Just asking because I saw Thomas' email
<https://lists.w3.org/Archives/Public/public-rdf-star/2021May/0023.html> about
the topic.

Regards
Anthony