Hello,
We tried to do several italian airports in the past: Reggio Calabria, Torino, Bologna, Florence and Rome were published by LAGO. Pisa, Aviano and Rivolto were published by Cloud9. Florence for FSX was published by Aerosoft.
The only one that didn't had very disappointing sales (guess what) was Aviano, because is probably the most appealing for the international public.
About FCO, the airport is surely the most important in Italy, but it's a large project and, considering past sales of italian airports, we might risk working at it for about the same time than KORD or KJFK, and selling only a fraction.