I don't think that the runway is the problem. I think the issue is that there simply isn't a market there. HVN is in the middle of a pretty dense area of other airports. Within a two hour drive there is an enormous amount of capacity:
New Haven as a city itself isn't that big and the overall cachement area that HVN covers has too many other options available to make growth at the airport compelling.
Pretty much the
same discussion as 3.5 years ago.