A capital gain is a capital gain. I don't think the IRS much cares if it is a pain in the ass for you to calculate.
I imagine they care about as much as I care that their tax laws will soon be virtually impossible to effectively enforce.
You're right there is going to be a lot of BTC gains that don't get reported to the IRS. All that I'm saying is that if you get caught then the "it was too complicated so I didn't report it" excuse isn't going to help you.