Good question.

As I said before and will probably say again, I'm not a lawyer. So, my thinking-as-the-plaintiff's-lawyer is prolly defective in subtle ways.

To gab about the defense side, it occurred to me that there's a two-pronged slam-bang defense that any real lawyer would bring up in the initial interview:

Prong 1: The Good Samaritan defense. The white-hat hacker team had no motive other than to rescue The DAO stakeholders and worked for free during their rescue operation. It's not enough to claim that they did so because they themselves were stakeholders - not as long as they got the exact same aliquot-share reward as someone who occasionally cheered them on at Reddit but otherwise did nothing. In order to impugn this defense, the plaintiff has to prove that they got compensation over and above what they got as DAO stakeholders. To put it bluntly, the plaintiff would have to show that they were either a) paid for the work, which would render the Good-Samaritan part of the defense moot; or b) that they were bribed to do it. Either attempt requires the plaintiff to have evidence; speculation won't do.

Prong 2: "We Haven't Touched The Ethereum Classic Blockchain" defense. This one's intriguing, because a court would have to regard the Ethereum Classic blockchain as a separate entity. If the defense can demonstrate that they haven't touched the Ethereum Classic blockchain, then the plaintiff's job becomes harder. Plaintiff would have to argue that the white-hat-hacker team had an affirmative responsibility to return the Ethereum Classic to the now-Classic-DAO token holders. This could be done, using that corporate-spinoff analogy I riffed on above, but it would have to be done carefully. A judge might well decide that the people who incurred the liability were the dev team behind Ethereum Classic!

In fact, Prong 2 might well suffice on those last grounds.

So a real lawyer for the plaintiff would ask: 1) "Can you prove that the whit-hat hackers received special compensation over and above their share as DAO token holders?" 2) "Can you prove that they messed around with the Ethereum-Classic DAO on or after the time of the hardfork?" If the answer to both is "No," then said lawyer would decline the case.

Or recommend that the plaintiffs sure the devs of Ethereum Classic!