I honestly think that would too restrictive. I think there should be some affinity with the country you play for, like a 2 year old immigrant knowing nothing but living in a country, or the child of English parents being born in Germany cos they were in the Army or something, but they move back when he is 1. Residency qualification is bollocks IMO, (that lad at Utd? He is not English. At all).
Going back to Grandparents I can live with tbh. John Hartson could have played for England, (not saying he would have though), and he said when asked why he chose Wales, "Because Im Welsh".