Strategy is outlined here:
Using Leveraged ETFs To Game The Roth IRA Maximum
Essentially, you keep 1/3 of your portfolio in a 3x leveraged ETF and 2/3 in cash. The author claims this combination (with sufficiently regular rebalancing) behaves the same as 100% in the underlying index of the ETF.
The advantage being that you can hold the 1/3rd inside an IRA and have the cash 2/3rds outside, effectively tripling your IRA contribution maximum compared to investing 100% in the unleveraged index ETF inside the IRA.
I'm wondering if there are any obvious problems with this strategy? The author outlines a few (transaction costs, underexposure to the index when it falls very rapidly) but they don't seem to outweigh the benefit of 3x contribution to a tax-free account.