Still makes no sense. OP demands introduction of different runtime semantics, but this doesn't require adding more language constructs (TS-like superset). Current type hints provide all necessary info on the language level, and it is a matter of implementation to use them or not.

From all posts it looks like what OP wants is a different language that looks somewhat like Python syntax-wise, so calling for "backwards-compatible" superset is pointless, because stuff that is being demanded would break compatibility by necessity.