Oh, I see, yes, you're right, you can recover the rest of the call stack with THIS CALLER. I forgot about that.
Oh I see, it bothers you that the syntax tree treats calls to a variadic block with different numbers of inputs as different. I might not have made that choice, but I believe Jens is following the same logic that's used to decide whether to populate empty input slots when a procedure is RUN or CALLed, i.e., the number of empty slots has to equal the number of available actual input values.