No country based seller could guarantee a 3 day delivery so it would wipe out just about everyone of them as

they would have to send express and that would make postage too high.

Sellers from WA or sellers sending to WA would also fall into the same category.

Another ludicrous decision to try and make buyers happy but stab sellers in the back again,

It might suit a small amount of sellers that use the express option as their standard postage.