If it happens, it'll be interesting how FR , through Beauvais, will reply to this
Why would they, there is currently an FR service to other airports in London from SNN, Heathrow is being held up by the lobby groups as the hub link for onward connection from the region. Similiarly CDG with WX would be a hub link, where as Beauvais would no doubt retain the loco traveller. Don't really see a WX service as being a threat in any real sense to the existing FR services, would suspect the price point would be higher and targetting the "onward connection" market or those not wanting to commute into Paris.
The key question remains unanswered ... is there sufficient onward connection traffic originating in/transiting to Shannon to justify such a service or was the majority of the LHR traffic starting/remainig in the London and SE England area. My suspicion is that it was.
JAS