I suppose the one thing that has changed is the economic situation although currently there is some doom and gloom about Europe in particular.
The business/first cabin of the CO to EWR was not used in the numbers it should have been if the route demands of the local business community had proved to be soundly based - but it's probably ever thus when airports conduct surveys of their local actual and potential clientele.
With a certain amount of devil's advocacy, but not entirely, I wonder how valuable a single daily rotation even to somewhere as high profile as New York is to the West Country's economy. The Bristol city region continues to be one of the UK's most successful and vibrant economies: would a daily NYC flight really make that much difference?
The CO route was fine for the New York area but anywhere else in the USA entailed a change of aircraft and often a long wait at EWR in at least one direction. What's the difference in flying to AMS, DUB or BRU and changing aircraft there with a wait?
The chief obstacle though is and will remain LHR, even with all the current argument about its future development, with its myriad worldwide routes, airlines and frequencies. Major M4 accidents and signal problems on the Great Western main line notwithstanding, LHR is very convenient for the Bristol area and nothing reasonably forseeable locally will ever make the tiniest dent in that situation. With electrification of the GW main line now under way and talk of a LHR rail spur the UK's largest airport could become even easier to reach from the West Country
BRS is very good at what it already does. Given its physical disadvantages it punches above its weight and I wonder whether it isn't a better idea to concentrate on continuing to build on that rather than look for NYC and MEB3 routes.