I thought about opening a IRA and then I found out you can only deposit a certain % of your reported income per year...I'll stick to my pile of BTCs the gov doesnt know about yet.
You only run into a problem when you eventually want to purchase something or exchange those bitcoins for dollars. When the tax man comes sniffing around, you're going to really wish you'd thought about the consequences sooner. You will probably wind up paying lots of capital gains taxes rather than risk jail time.
You can put $5500 (or $6500 if you're over 50) per year into a Roth, up to 100% of your taxable income. If the price of bitcoin really explodes, you could someday save $100,000 in taxes.