The only way for Federer to be a worthy GOAT candidate of any degree would be to:
-Win atleast 2 Calender Slams
-Wins slams over a 12 year span/13 year stretch so win atleast 1 slam in 2015
-Gain a winning head to head with his main rival Nadal in slams, so gain atleast 5 more wins vs Rafa in slams than Nadal can on him
-Beats Nadal in a French Open final atleast once
-End the year ranked #1 atleast 3 more times
-Gains a winning head to head with Murray, not even strictly the slams is good enough in this case but overall
If he achieves this it would put him in the conversation with Laver, Sampras, Rosewall, Gonzales, and Borg. Right now he is in the second tier with people like Tilden, Budge, Kramer, and Perry; just above the 3rd tier of Lendl, Connors, McEnroe, Cochet, LaCoste.
First of all, I think the whole goat conversation is a complete waste of time, and energy.
This list is pretty amazing. You are asking of Federer more that any of the others accomplished to allow him to achieve status with them. Do you really think hasn't already accomplished more than all but perhaps 2 or 3 of your listed players?
Secondly, Keep in mind that the US Open and Australian Open were played on grass when Laver won his two grand slams. So technically, he won the Grand Slam, but never won a grand slam on a hard court (not that he could have if he tried). Graf's 1986 Super Slam is really the only true Grand Slam where she won all the tournaments in their current configuration.
But that's enough of my goat talk. Keep thinking... maybe you can invent a couple more requirements over the next few months.