Yeah if you've ever bought MLPs before in a taxable account, you'll see that most of them don't generate very much 'income.' It's amazing the accounting wizardry they do to lower the investor's taxable income on the K-1.
As far as holding MLPs in a retirement account, it's true that the rules say UBTI over $1k is taxable. However, I'd like to know the number of investors that would actually have that much in MLPs to do it. A prudent investor that is not an industry expert would never hold more than 5-10% of their account in MLPs. If those MLPs on average are distributing 5%, you'd need a $20k investment to generate that kind of UBTI. If MLPs are 10% of your account, that means you'd need an account of $200k before worrying about UBTI.
Honestly I don't know if this is much of an issue for a lot of people on this board.
In reality, I'd be surprised if your broker/retirement account even keeps up with UBTI. And beyond that, good luck finding two people at the IRS that even knows what the acronyms MLP and UBTI mean. My grandfather, who spent his career as a tax accountant for oil and gas pipeline companies, finally realized he would never be audited by the IRS because nobody there understood it. He holds crazy amounts of MLPs in his IRAs and just pays the taxes when he takes out the money like normal.