As an Australian, with friends who work for banks and major accounting firms - I *honestly* can't see this being approved by our government. The big banks here flag all BTC transactions as possible fraud, and ASIC (the government body that regulates companies) hasn't got many good things to say about BTC.
Actually, most Australian banks are Bitcoin-friendly (I think Commbank is about the only one that isn't), and ASIC (along with AUSTRAC and ATO) have been pretty neutral.
Our GST is at 10% - so currently, selling 1 x BTC (~$750 AUD today) - would require the company/customer to pay $75 GST - which means the total cost for the customer would be $750 + $75 = $825. Who would buy a BTC worth $750 for $825?
Nobody, but not because of the price. Nobody would buy BTC from an exchange so incompetent that they don't know that financial instruments are except from GST. Only trading fees are subject to GST. Why do you think Australian bitcoin exchanges haven't been shut down by the ATO?
Exchange rate vs income tax. Any money a person makes from BTC will need to be taxed, how are they going to tax it? Are they going to calculate your net worth from your holdings of BTC like they do with shares? If you buy 10 coins at $1000 AUD - and they jump to $20,000 AUD each around tax time - do we need to pay capital gains tax on $200,000 AUD - even though the bitcoins haven't been sold for AUD?
No. You only owe capital gains tax when/if you sell or otherwise trade your bitcoins.
Interest Rates - If someone gets a BTC credit card or loan - how do they pay the interest on that or deal with huge price increases? Same figures again, imagine we get a loan for 2 x BTC ($2000), and the price jumps from $1k to $20k - without direct access to BTC, does it mean their debt will have gone from $2k to $40k ?
Yes.
How does a customer obtain the ~0.01 BTC required for interest? do they need to buy BTC and pay the bank with that - or do they need to pay in AUD for the hugely inflated interest price?
The former would probably be preferred, but either way would likely be acceptable.