I would tend to agree with connections via LCY, I dont think that you can say people who connect go via LHR.
Im fairly certain that people connect onto the BA1-4 services from EDI, GLA etc. I know that if BA ran domestic flights from NQY-LCY i would look at connecting at LCY if heading to NYC.
The one thing i would guess that would put people off would be the lack of a Galleries lounge.
I do think that BA Cityflyer will continue to expand at LCY, and i think that JER & NQY could be the next destinations, JER especially as BA already has a presence at JER, no need for lounge facilities, SSCI machines, handling contracts etc. Same as ABZ really
cs