This cannot be done with a function, because function arguments have to be evaluated before the function is called. In other words, they are eagerly evaluated.
Like the ternary if, and and or, this has to be lazy and only evaluate the right operand if the left operand is None.
PEP 505 suggests three new operators, ??, “maybe dot” and “maybe subscript”. If you want to propose alternative spelling that doesn’t use a question mark, you need to propose an alternative for all three, not just ??.