I booked my first long haul with ITA a couple of days ago and used my SEN number as FFP. When I went to check about seat selection, there were fees all around and on the long haul leg the system was asking between 120 and 300 eur .
I had to call ITA for another thing related to that trip, and once solved, I asked about the seating, the agent told me there is no recognition yet for the SEN about seating fees but maybe between here and the time of the trip (after summer) there will be something in place.

I hope LHG will work that out soon.