Some here should really read the article. There would not be a separate "Bitcoin tax", but:
The current plan includes taxation of capital gains, imposing VAT, and gift tax
That would mean, like @entrepmind23 already supposed, that they would treat Bitcoin like other financial assets. In Germany for example, it's similar, too.
There would be nothing special about BTC: If you hold/trade Bitcoin (like a stock) and make profits, and these are larger than a possible "tax-free profit", then you must pay capital gains tax. Or if you're a merchant and sell a good or service for Bitcoin, then you must charge VAT.
And with respect to "they cannot track it": It would be similar as with cash. If they detect large movements and suspect you to hide them, they could request a raid and analyze your computer(s) for possible wallets.