As a matter of interest, how many T21 rail projects are financially, as opposed to economically, viable? Pace isn't (http://www.meathontrack.com/uploads/...rt.pdf#page=26
) and neither is Midleton (I can no longer locate the study online, but it's discussed on pages vii and viii, or 7 and 8 of the pdf - and probably at greater length elsewhere - for anybody with a saved or paper copy; the study states that "there are few rail projects which can be justified solely on financial grounds"). I think I remember reading somewhere that the only project emerging from the Dublin Suburban Rail Strategic Review as financially viable was the Phoenix Park Tunnel.
It might be that the economic results were unsatisfactory, but nobody's actually said so. Of course, the points about costings and population growth are valid ones.