Of all the tournaments Rafael Nadal could have made his return at, the VTR Open in the Chilean resort town of Vina del Mar is one of the least likely, based on the Spaniard's scheduling history.

Nadal hasn't played any South American event since 2005, when he won Costa do Sauipe to begin his worldwide chase of clay-court titles. But with Rafa ready to get on the court, and it makes sense that he'd want to start his comeback on clay. Thus, this small but fortuitously-positioned event has been visited by the greatest dirtballer of all time.  
Nadal's South American sojourn got me thinking: What other unlikely tennis happenings might come to pass under the right circumstances?  
Here are three, all quite inconceivable at the moment—but in sports, you can never say never.  

Roger Federer plays Newport: This is the grass-court equivalent of Rafa's visit to Vina del Mar. The Hall of Fame Tennis Championships in Newport, RI is one of just six grass-court tournaments on the ATP calendar, but it's the only one held after Wimbledon.

As such, Newport rarely boasts a strong field, contested mostly by Americans and players outside the Top 10 who didn't fare well at the All England Club.  
The venue—on the grounds of the International Tennis Hall of Fame, as you might guess—can't be beat, and the tournament's history shines no matter who comes to play, with grass courts abutting the show court on each side, and well-heeled New Englanders shaded underneath green-and-white awnings.  
But even for a history buff like Federer, Newport probably doesn't offer enough incentive. He almost always takes an extended break after Wimbledon, his favorite tournament, and traditionally waits for the Canadian Masters to cross the Atlantic.  
There's also the fact that Newport is just an ATP 250; even a title run would barely register in Federer's often voluminous mid-summer point total. Only if Federer wants to make nice with the induction committee will we see him in Rhode Island, but we all know that's unnecessary for the 17-time Grand Slam champ.  

The Williams sisters play Indian Wells: For an entirely different reason, it's unlikely that we'll see Venus Williams and Serena Williams playing at the BNP Paribas Open.

Joel Drucker does an excellent job of recapping the controversy here. Essentially, neither sister has played Indian Wells since 2001, when Venus pulled out of a semifinal with Serena just four minutes before their match.  
Afterward, Richard Williams, Venus' and Serena's father, was accused of orchestrating the withdrawal, and was allegedly the target of racist remarks during the final. Serena was booed heavily throughout the match, and later said she would not play Indian Wells in the future.  
More than a decade has passed since the incident, and there's been nothing to suggest that the Williamses will return to Indian Wells any time soon. Furthermore, there are a dwindling number of seasons remaining in the sisters' playing careers, so if they wanted to do an about face and enter the event, the clock is ticking.  
From a calendar standpoint, Venus and Serena have already committed to the Family Circle Cup in Charleston, which is played directly after the Sony Open in Key Biscayne, a U.S. hard-court tournament they've always entered. Miami may not have Roger Federer this year, but it will have Venus and Serena, something Indian Wells may never be able to say.  

The Davis Cup comes to Forest Hills: This takes wishful thinking to an entirely new level. The West Side Tennis Club—colloquially referred to as Forest Hills—has seen far better days from a pro tennis standpoint. (As a club for recreational players, it's still lovely.)

The last tour-level event held there was in 2008, a 16-player WTA tournament, and you could literally count the number of patrons inside the dilapidated stadium.  
That stadium, of course, played host to the U.S. Open before it moved to Flushing Meadows. But while players and fans from around the world now descend on the National Tennis Center, which boasts greater amenities, better sightlines, and ample parking, history will never leave West Side's stadium.  
Its stands require substantial repair, but a gleaming hard court is already there, and all you need is one of those in a Davis Cup tie. The Winter Olympics probably have a better chance of returning to Lake Placid, but if the USTA decided to get nostalgic, I can think of no better place to host the competition.  
Oh, and if U.S. captain Jim Courier wanted to stage a tie on grass? Forest Hills has those courts, too.