AFAIK there has been no claim, successful or not, reported. Unsurprisingly, as the SWISS position is that the ticket was not valid. EU261 was not established to resolve contractual disputes.

It would be a simple matter to consult any of the companies handling EU261 claims on a "no win, no fee" basis (e.g. http://www.euclaim.co.uk/ as one of many). They will advise on the chances of success.

Otherwise a direct approach to SWISS will most certainly be kicked back, leaving the national enforcement bodies or court as the next available steps.

Note that any statutory payment under EU261 would most likely be reduced, $ for $, by related payments received elsewhere.