*Sigh*
I would just like to comment as a perosn who has had expirience in these matters and as the one who came up with the regions/districts method.
The whole point of doing it liek this was to assure that we had Senators who were responsive both to small regional interests, and to population (like the real Congress, but unicameral). Also, it assures a higher level of political variability. You can't keep changing the Constitution ever time it suits you, less it becomes meaningless, as it did for me when I was involved.
This is not to mention that, against my advice, they already got rid of the current system once, but ended up going back to it, as they found it was the best way to go.
I think that the idea is for the five single member districts to be replaced with one multi-member district elected by STV.
At least I hope so; ten regional senators is a ghastly prospect.