As Tolmie mentioned yesterday, I think the lack of a deal is down to relative valuations and player salary (FDJ is owed something like 14m in deferred wages). Tolmie has Barça valuing FDJ at 80m and Bernie at 65m with City seeing it exactly the opposite.
Seems like Barça want the buying club to cover the deferred wages in addition to paying full price, whereas City, and other interested clubs, are only willing to go up to 80m, all in. Probably the only way a straight swap can happen is if Barça agree on City's valuations and accept a big book loss on FDJ with City booking a massive (sic) profit for Bernie.