The point is that the part of mojo that is new allows you to write early bindings that can't change, immutable variables, values that are accessed without indirection, types, ownership annotations, etc, and uses all of that to do precisely what you are asking for.
If it can't do much until those extra annotations are in place, then I would imagine it's unlikely it'll ever get support from numpy, django, and the like. Uptake for mypy type annotations alone has been pretty slow.
