Okay so let me start off by saying there's not a high chance of this happening, but the point is is that there is A slight chance.
When Durant's contract is over, Masai should be heavily targeting him. Considering the timing and all the factors, I believe we'd have a top 2 shot of landing him.
Out of all teams, I think top five in 2015 to land KD are OKC, Toronto, Phoenix, Lakers and Philadelphia.
Let's start with Phili. The only way they pursue is if they don't draft Wiggins or Parker this year. If they elect to draft Embiid, their core is now MCW, Embiid and Nerlens Noel. They are in obvious need of a wing. With the progression of these players and their tons of cap space, they'd have a legit shot.
Next up: LAL
LA is automatically a player in every big free agent that's in play. They have Kobe and whoever they draft this year, and they would have a pretty good chance at signing him. The only thing that holds them back is Kobe's contract. Kevin Love is also a free agent that season, and seeing how he's a LA native, odds are they pursue him more. And quite frankly they can't afford both.
Phoenix is a player because they have so much versatility in their roster. They have two point guards that have star potential, and four first round picks in a loaded draft year is big. No one really knows what their roster will look like a year from now, but they will almost certainly have a solid core and cap space.
The obvious pick. KD has made multiple playoff runs and has a sidekick with Russell Westbrook. They have young players that can flourish in a couple years (Reggie Jackson, Jeremy Lamb, Stephen Adams) and odds are KD doesn't want to abandon that team or city.
We are an interesting team in this because it seems like we are building our team strictly to lure KD. Masai has said that Greivis Vasquez will be around for awhile as they have a relationship that goes back years to when Masai gave Gravy his big break. Vasquez played with KD in high school and so there's familiarity. Tim Leiweke has made a concentrated effort to fix the burnt bridges between Toronto and Carter, and whether Carter is back or not, he will most likely be more a part of Toronto's future in the coming years (throwback jerseys, ceremony and probably retiring his number). Where does Carter come into play with KD? KD has said that Carter was one of his favorite players growing up when he played for Toronto. Also, it's very clear that Toronto does not have a starting SF on the roster, Ross has been there but he is clearly not big enough to stay there long term as we saw in the Brooklyn series. With Ross being an obvious non-fit at SF, Masai has done nothing to try to fix this issue. Throw in the fact that Toronto has a rebranding and they host the allstar game the season after KD hits free agency, and the stage is pretty much set for this team to be his. Clearly, Toronto has a very real shot at landing him.
Out of all five teams the top two I would say are OKC and Toronto. Talking strictly basketball, I personally think he has a better shot at a title in Toronto.
OKC has made the finals once with Durant on the roster, and they had Harden on the team then. They are in the brink of a first round exit this year and the west is a very strong conference, leading to a harder path to the finals. Finally, KD-Westbrook is clearly not enough to win a title and there aren't enough shots (or money really) to go around to signing another big name player.
Toronto would be coming off of their second competitive season, but their roster would suit him perfectly. A starting lineup of Lowry-DD-KD-Amir-Jonas is dangerous and a bench with Vasquez, Ross, Patterson and our draft picks (our 1st rounder this year, our 1st next year and NY's 1st next year). Being in the east pretty much means you need to be able to beat Miami to make the finals and I think that roster would 2 years from now. KD would have a legitimate shot at a title and he'd be the face of a roster on the rise, so I think he'd be best suited to choose Toronto. And seeing what happened with Lebron winning at least 2 titles since switching teams (possibly 4 by the time KD makes his decision), clearly winning is a bigger factor then loyalty.
TL;DR Toronto has a legit shot at signing Durant when his contract's up and should try to land him by doing whatever it takes.