Players playing for two countries
Saqlain Mushtaq is talking about playing for England. Much as I'd love to see Panesar/Saqlain bowling at either end for England in terms of the quality of their bowling, it's just not right.
You can't play 49 games for Pakistan and then play for England. Or play for Australia and then South Africa like Kepler Wessels. None of that should be allowed. One country for life I'm afraid.
That said, Ryan Giggs playing for England youth, and then for Wales full team, seems ok to me - I think you should be allowed to play where you live until adulthood. Although it doesn't work the other way round - Clive Woodward wasn't allowed to play rugby for Wales Schools in his youth as he is English, despite attending a Welsh school.