With Flybe offering less seats to Palma on the DHC 8 compared to last year on the EMB 195 I shouldn't think it will be a problem filling the aircraft.
The price difference between Volotea and Flybe to Palma is incredible and I only hope that the former make a success on their new operation from SOU and hopefully expand for summer 2017.
The fact that Flybe are using a DHC 8 on the Palma route in 2016 may actually deter passengers from booking especially as regulars on the route have been used to flying the EMB 195 and even more so now Volotea are around offering a jet service and undercutting the extremely high fares that Flybe charge.