As an Australian, I'm happy to hear this, but also annoyed that a lot of legitimate SMS from companies don't use branded sender ID. I'm not sure why, but my guess is that SMS gateways charge more for it and businesses don't want to pay the extra cent or two.

Alpha codes don't allow replies. As such if you need to reply it has to be from a number

No it costs the same, the reason they do it is that it’s slightly more difficult to spoof a real number sender ID because most gateways will verify ownership by sending you a text on that number before letting you send outbound from it, where as they have no way of doing the same for an alphanumeric sender ID

That will likely change after this goes into effect, otherwise all that legitimate spam will never make it.