I don't know the details but from what I read of the linked pdf my feeling is that they don't have a case. Sanders knew the rules when he decided to run for the DNC nomination. Maybe our resident potsmoking, Hudsonlover, fabulous lawyer poster will have more information, but I think it's a waste of time and money.
I think their argument is that the attached document shows that the DNC never considered the possibility of a non-Clinton candidacy (referring to the race as "GOP nominee vs. HRC" rather than "our nominee" or "Dem nominee" which combined with the black magic of exit poll discrepancies CLEARLY shows the DNC was in cahoots with the Clinton campaign to destroy Sanders from the beginning, and it was only through his own personal ingenuity and the complete lack of Clinton supporters that Sanders was "allowed" to win any states at all.