An ATR for CGN makes sense, it's not far.
I wouldn't underestimate the power of social media in promoting the airport. Just look at what Trump 'achieved' with a daily deluge of tweets. Rather than wrap a train, I'd like to see more advertising inside the carriages of mainline and underground services that serve Essex and East London. Perhaps with a code to quote for a 5% discount on Flybe flights. Lots of travel related businesses do it, and have done so for years, so it may prove effective.