You mean like:

  repeated oneof actions {
    ActionTypeOne type_one;
    ActionTypeTwo type_two;
  }

or like:

  oneof thingy {
    repeated string first_option;
    string second_option;
  }

I can see why you'd want to do either of those things, but it doesn't seem like a huge deal to me to wrap those in another message.

And why can't you wrap it in another message?