I disagreed in terms of what it would mean if he had the slam. I don't think Federer is the GOAT yet, there are still things he needs to do. I'm a big fan, and I do believe he will be able to surpass the overall total. And in many ways to me he's already demonstated just how dominating he can be.
However, here is why I think he needs the grand slam. And I agree that it doesn't need to be in the calendar year. Right now just on this board alone there is a huge debate of who is GOAT. Along with Federer, the other 3 names that are usually mentioned are Laver, Borg and Sampras. Laver has the grand slam, Sampras has the overall total of slams, and Borg has the number of Wimbledons in row, plus being able to win the French in the same year. If Federer gets the slam this year, that will take care of what Laver has over him. In winning the French Open this will basically take care of Borg as he will surpass Borg number of slams, he will also tie Borg with 5 Wimbledons and have a French the same year. To me this will pretty much take Borg out. So this leaves Sampras. Federer will now have something Sampras doesn't have which is the french open, and it will bring his total to 13 slams. He will only need 2 more slams and that will take care of Sampras.
Without the grandslam, it will still come down to how much does the French Open count and should it just be total. With the grandslam all of the questions go away.
Jukka