And while the YE #1 might not be the highest priority, Federer is well aware of the fact that a sixth would tie the record. He likes records.
Not even talking of records, finishing the year at number 1 at 31 years old in a very physical era and with such competitors as Djokovic, Nadal and Murray, even though they're not at their best (although in their prime years
), would be just incredible and would fully achieve the "back to youth" story at an old age which this year looks like for him.
And if you speak of records, no player has finished the year at number 1 after 30 years old since the creation of the ATP rankings (Agassi was number 1 at 33 years old but for 3 months only, and Connors did not finish the year at number 1 in 1982 : he won 2 slams but McEnroe got more points in other tournaments).
But it would be really meaningful only if he won the US Open (and anyway if Djokovic didn't win the US Open, because if ever Fed managed to achieve the number 1 whereas Djoko won the US Open, I don't think Fed would really feel as the number 1 and people would always contest a lot about that, which is not good for pleasure)
PS : thinking Fed is mostly drawn by records is wrong if you hear him and Paul Annacone correctly, he's mostly driven by the pleasure, the titles and the fans' love. He just says "it's nice" when people talk to him of a new record he's just achieved, it's just part of the pleasure but he's not obsessed about numbers.