Why would the States be interested in spending money on having jets flying the route? It is not as if Flybe would not have any suitable equipment to operate to GCI. They could always use the Q400. It is a difference of 30 seats per flight and in total a loss of 120 seats a day. This could be off-set by an additional rotation. If LGW slots do not permit for that, I guess combined loads on BE and GR are not that spectacular that the island would face major problems (the morning flight out of GCI might be bit tricky, though).
On the other hand, 120 seats would be a nice 4 times daily Cityjet Dornier operation to LCY - maybe something the States are hoping for (if the whole exercise of not letting the E195 into GCI is not just a poorly disguised support for Aurigny).