I feel like if this scenario were to happen, Nadal would well likely surpassed Federer in the GOAT debate as well as cementing 2017 as one of the greatest tennis seasons of all time for him.
There's no legitimate GOAT debate currently. Nadal would still be behind Federer in almost every major criteria even with another three Slams.
On-topic, of course Nadal came close at the Australian and is now the favourite to win this (heavily asterisked) USO, so a three Slam year was theoretically plausible. I don't think he had any chance at Wimbledon though.