FWIW: Go's switch statements are break by default, with an explicit 'fallthrough' keyword if one wishes to override that behaviour.

The only real case I use switch fallthrough for is when you have two cases with the same code, e.g.:

  switch (foo) {
  case 1:
  case 2:
    /* common body */
    break;
  case 3:
    /* body 3 */
    break;
  }

It's not cognitively hard to make an empty case body fallthrough to the next run, but include an implicit break at the end of every nontrivial body.

Supporting Duff's Device is not a compelling feature to support--irreducible loops are basically going to destroy any hope of optimization you might accrue.

> But then you would need 'unbreak' or just 'goto' to the next case. No duffs device no cigar.

From Algol's linage point of view, a very good outcome.

Yes, but you would need way fewer of such phrases than you need now. Making the exceptional case take more code is the way to go, IMO.

Many languages also support something like

  case 1,2,4:

or even

  case 1-10, 20-22, 34:

That further decreases the need for falling through.