if doesn’t add much imo (I prefer case) and the implicit else clause is not obvious to newcomers.
I would also remove the restriction that string keys must precede atom keys in map literals. i.e.
iex> %{"a" => 1, b: 1}
%{"a" => 1}
iex> %{a: 1, "b" => 1}
** (SyntaxError) iex:3: syntax error before: "b"
For a beginner this can be a bit of a wtf moment! 
