The real reason this is bad is for miners is that it could greatly increase the risk. The IRS just said you are taxed at the rate when you receive the coin. What happens if the coin loses value from the point when it's mined to the point when you sell it?
Lets say I mine 1 btc on a pool and the pool sends me the BTC. I have a record of the transaction being sent to my wallet. I can then look up the value on bitstamp at the time I received the BTC, lets say it's worth $580. The IRS says I'm taxed on the $580 as "income" minus any expenses such as cost of miner and electricity. Now I wait 6 months and the coin I mined is only worth $200 and I sell. The question becomes, have I just realized a $380 capital loss to adjust income? This is the big question I have from reading the IRS FAQ.
There are TWO taxable events. The first is at the point you had taxable income, the second is at the time of the sale.
To expand on your example:
Say you mined 1 BTC today and the current exchange rate is $580. That would be $580 in "regular income". You can file this as a business and reduce that by the electricity and amortized hardware cost. Lets say your costs are $320. You would file a Schedule C report the income, your expenses (like electricity) and the depreciation on your miner. Lets pretend it works out to $320. Then you would have a net income of $580 -$320 = $260 added to your other income (wages, tips, interest) and it would be taxed at your normal tax rate.
Now if you sold that coin today as well then you would have NO capital gain. However lets say you held on to that 1 BTC for three months and when you sold it you got $900. You would have a capital gain on the GAIN over the $580. So $900 - $580 = $420. On the other hand lets say the price had declined and you sold it for only $400. You would have a capital loss of $180 ($400 - $580 = -$180). The capital loss can offset capital gains and up to $3K can be applied against "regular income", the rest rolls forward to the next year. If the time between mining and selling was greater than a year then those would be long term capital gains/losses otherwise they are short term capital gains/losses.
Note this isn't legal advice just trying to parse out what the IRS said. It also doesn't mean I agree with any of it. Just going by what was written and pointing out it is possible for there to be two taxable events. It is very likely the IRS will need to provide some concrete examples with figures before this debate it put to rest.