In some ways, this is just as esoteric as it sounds. Federal courts can hear state-law-based claims, but only when they have a basis for jurisdiction. Certain kinds of claims can never be heard in federal court, such as determination of child custody. Most of the time, though, one must have enough at issue to make it "worthwhile." The question is whether each person named (or, more to my interest, each class member in a class action) must individually have that much at issue; and, if not, whether all parties can aggregate their claims, or rely on one party having that amount at issue and ride in on the coattails. Unfortunately, the statute in question is not crystal-clear. On the other hand, neither is the silly concept of measuring somebody's ability to use federal court by whether one can put a given dollar value on his/her claim.
In any event, this matter arises from a product-liability suit. A little girl in Puerto Rico slit her hand on a tuna can. In a tortured (and ultimately unpersuasive) opinion, the First Circuit ruled that she could meet the jurisdictional minimum, but that her parents' pendant claims could not. And, as one looks more closely at the legal context and the facts asserted in the complaint, it gets even sillier. But, as silly as it is, it needs to be resolved.
I predict that the Court will punt the general issue. It will probably find a reason to treat this matter as sui generis, because the girl can't sue by herself anyway—she can sue only with the legal assistance of her parents, because she's not 18. It would be better for the Court to step in and state the general rule; but it has been loathe to do so on matters of jurisdiction that are not related to the Eleventh Amendment (just look at the tortured reasoning in last spring's detainee cases).