Basically, the authors endorse a federal law allowing U.S. citizens who've been sued overseas to countersue here. Often, they admit, this will result in a useless verdict — if you win your countersuit, you can't collect until the defendant comes into the U.S. However, people who file libel suits against U.S. citizens in other countries, and then lose countersuits in American courts, won't be able to come here without paying up.
I agree that this is sensible, but I'd like to stress something the WSJ authors didn't see fit to mention, and often gets conveniently left out when people seek to depict "libel tourism" as a serious threat: U.S. courts, as a practice, do not enforce foreign libel judgments that are inconsistent with the First Amendment. I'm fine with codifying that, or with making sure people who engage in libel tourism never set foot in the U.S. — but this is a safeguard, not a response to some huge threat. I argued this here and here also.