From the recently published article, it seems the mood is very positive that the link will happen. The space is there and available next to Parkway station, the challenge he airport end but the tunnel was built with a rail link in mind so perhaps they will revert to that plan?
Given the growth of the airport the need for for a link is all the more urgent. As the airports biggest operator, easyJet are clearly pushing hard for it according to the article and the airport clearly wants it so hopefully it will happen as is intimated