It makes huge business sense for City Types who believe their time is money.
32 searter A318 parked down in LCY, proposal I believe is check in closes 30 mins before take off. Hop to Shannon to re-fuel for TA and do US boarder controls (and soon customers) clearance, pop to JFK, swan through the crowds and into your waiting taxi/limo.
Compare that to fight your way from the Canary Warf/City to Heathrow. Check in 2 hours prior to take off, queue through LHR security, sit in the lounge, queue onto Aircraft, taxi to runway, queue for take off and then to JFK. Queue for passport control and then queue for customs.
I suspect time from London desk to kerb side in JFK with the new LCY/A318 service will be shorter than traditional services.
Sounds like a brilliant bit of lateral thinking to me.
JAS