the pod was 1850, so avoiding some of the great famine (1845-1852) would have hugely increased irelands population.I would have to say Ireland had other policies been taken post '22 (leaving aside of course a different outcome to the famine), a stronger economy would have reduced emigration which would have strengthened the economy and so on (for example with the stronger economy of the last 2 decades and predictions of the 2, the population has grown by over a million and predicted to grow by another million by 2040).
the population of ireland (whole) in 1841 was 8,2M and 4,4M in 1921 (3M for Eire in 1922). so with no famine and ireland (republic) could be at 6-8M. with a limited famine 1M more population isn't unrealistic