It is only remarkable that they have not done this before and they should concentrate on this kind of operation, rather than the 75 ops from Paris.
On this route, they have no competition and retain their core users. Paris (and other starting points) are the opposite.
The big problem at the moment is fuel costs but, for as long as they remain the only carrier on that route, the extra costs will not notice. As has been said, the potential clients will have said Yes to this two years ago. Not least evidenced by the retention of domestic services into LCY when they abandoned the rest of the domestic network.
I don't think SilverJet have much to worry about as they have a different catchment area and a different slate of pax.