Would a win in Lamberth court provide a possible class action suit by fannie commons? Maybe Ackman would take the lead.
It's possible, but that's also a very silly risk for FNMA holders to take. Winning in Lamberth's court guarantees damages to FMCC holders, while a similar, later lawsuit by FNMA holders runs the chance of failing.
There is no reason for FNMA holders to not switch all their holdings over to FMCC right now. The potential damages for FMCC greatly outweigh any tax considerations.