Just looking at the BMI Regional website and the price of flights are eye watering particularly compared with the Ryanair fares that the public have gotten used to.
The PSO will not be subject to APD which may help a bit but it could still be relatively expensive. Other routes would be subject to APD.
It seems to be business orientated and definitely not attractive for a weekend away. Certainly LDY needs business friendly services and that was missing previously but now the airport will be missing the large volume low cost passengers.
I reckon there is a fair chance the route is going to fail and in doing so will cause irreparable damage to any last shreds of credibility that the airport has.