FR24 doesn't quote any source for the 3-engine-ferry scenario (and I doubt they have access to any inside information) so that likely comes from the same source (Reuters) that originally quoted speculation about the recovery by an unnamed investigator from the BEA (who won't have any say in how it's done).
AFAIK there has been no subsequent announcement from those who will decide - the airline and the regulator - in support of that proposition, so don't be surprised if the aircraft finally departs with a full complement of operating engines.