Much could be done now to speed up the link. First scrap the extra charge for the shuttle bus. This can add minutes as most passengers don't seem to buy through tickets. Increase the frequency of the link is another. The problem is that the airport now has no control over the link although I suspect they take a cut of the profits.
For the long term what it proposed will cost millions and will no doubt need another extension of the franchise.
Seeing how many years the existing airport upgrade has been talked about any meaningful replacement for the shuttle buses will be at least 10 years away.