I do think there is a chance of Aer Lingus Regional operating the route although would suspect it might be Cityjet operated rather than Stobart operated as Cityjet operate the existing London City route to Dublin.
I think Stobart would be crazy to attempt to operate under their own brand at the moment, but an Aer Lingus franchise might work.
I'm hoping, probably unrealistically, for BA Cityflyer on the route as it would open up the possibility of onward connections at London City as well as one and done traffic. BA don't seem interested in having franchisees these days (I know there is Sun Air and Comair) although BA Cityflyer does sometimes get other airlines such as Stobart, Loganair and Eastern to operate flights for them.
Aer Lingus Regional wouldn't offer the same in the way of connections as I don't think the current Dublin to London City Aer Lingus Regional flights are offered for sale on the BA website although I could well be wrong about that. To me much of the Aer Lingus Regional model seems to be based on providing feed for connections via Dublin with the one and done traffic being a bit of an add on to this. There is no opportunity for traffic connecting in BHD.
Just a wee note,
DUB-LCY with EI is bookable through BA’s website, came across it by accident a few days ago. 😀