Well, not far enough in terms of innovating/rediscovering tennis in these dull times of monotonous baseline rallies. But the question is specifically about Roger Federer's recent attempts at hyper-aggressive half-volley returns on opponent's (second) serves.
Federer, after Wimbledon, has on numerous occasions tried to charge towards the service line to take the returns early to unsettle the opponents. While the attempt is nothing new, Serena Williams stands well inside the baseline against weak servers & thumps return winners.
But nobody has reached as far ahead as Federer has. He has taken the returns almost at the service line. So 3 questions.
1) In any of his attempts, has the point of impact with the racquet been inside the service box?
2) If NO, then, is having the point of impact inside the service box legal in tennis rules?
3) If YES, then can he essentially, stand at the net & volley the opponent's serves, from the rules point of view?