FWIW, I could personally tolerate the introduction of s{} and fs{} literals. We'd just declare the "s" prefix optional for non-empty sets to match the current rules.

Encouraging the use of ast.literal_eval() over the security nightmare that is eval() would be more than enough justification for me. (As a syntax change, the idea would still need a PEP, though)

Cheers,
Nick.