It makes this a very high stakes game, since even if the court throws out the result of the subpoena for use in the libel case, Prenda gets what they want. You could argue that is why they filed three separate actions in three different courts, just to up the odds that one of them would get the desired information.
They've done very similar things before, where they filed a lawsuit against the same list of IP addresses / John Does in a dozen different venues, because they only needed one judge to allow the discovery request to go through to get what they wanted.
It looks like they domesticated it to California, so they (wordpress) would need to file a motion to quash.
...really swinging for the fences with this one.