Although this move prevents any possibility of the Michael Barone scenario, in which Puerto Rico could have been effectively a winner-take-all victory for Hillary Clinton (a scenario that I think wouldn’t have happened anyway), it’s nevertheless good news for Hillary in two ways:
First, it saves her from the embarrassing predicament of relying on a last-minute caucus blowout in Puerto Rico to narrow Obama’s pledged-delegate lead, even as she’s arguing to the superdelegates that they should give less weight to his caucus victories than to her primary victories. (My dad alluded to this earlier today in comments.)
Second, it raises the possibility that Hillary can rack up a big popular-vote primary margin in what is presumably friendly electoral territory for her, thus increasing her chances of “winning” the overall “popular vote,” which, as I noted earlier, is absolutely crucial to her chances of convincing those supers to throw the nomination her way.
One other thing: this move is proof positive that jurisdictions are free to change the dates, and formats, of their nomination contests, even after the process has begun elsewhere. This is, of course, highly relevant to the Michigan and Florida “re-vote” debate. Some folks are arguing that MI and FL “re-votes” would unfairly “reward” those states for breaking the rules, because they’d be effectively positioning themselves as kingmakers. But the reality is, anybody who hasn’t yet held a (legitimate) primary or caucus can position themselves as kingmakers by moving belatedly to the suddenly attractive end of the line. For instance, if Mississippi wanted to move its primary to June, even at this late date, it theoretically could, under the DNC rules. The way I see it, Michigan and Florida, like Mississippi and Puerto Rico, have not yet begun their delegate-selection process. As such, they’re still free, under the rules, to pick whatever date they want, between now and June 10. That’s not a special reward for rule-breaking, it’s just straightforward application of the same rules that apply to everyone.