So this is one that won't happen, but serious consideration should be taken for it: Kyle Korver.
The things I would emphasize that would be important about this are 1) role, 2) familiarity, 3) fit, and 4) reputation.
This is not to diminish from Niang. I think Niang has given great effort, and he like others on the team (Conley, Bojan, Clarkson) who haven't been known for being defenders, are playing excellent team defense. I know there's an argument on the value of Niang's three point shooting and its impact on spacing and whatnot. But I think when we're talking about the difference between that and even Korver's reputation alone, these are worlds apart. I would be very interested in the number breakdown on Niang's percentages based on when he's being guarded. Niang has done really well shooting the three the prior two seasons (40% and 41%), but his attempts do appear mostly open. When Korver gets up threes, these are often contested or heavily contested, on the move, with a second or two on the clock, falling out of bounds, etc. When we traded for him, you would notice the defenders expending a lot of energy doing everything they could to stay with him. Now, you could say that our bench scoring sucked and so they could devote more resources to this strategy, but if defenses now have to devote energy elsewhere, well, then you're leaving open Korver. But Niang may draw the defense in the sense that maybe they'll try to close out more, but even by reputation alone, you'll see Korver stretch that quite a bit more. We're a great three point shooting team, but Korver is an all-time great, and because we have a lot of guys that can shoot, it opens up the floor for guys getting open looks. Korver is a guy who hits high percentages regardless of what kind of three he's putting up, and isn't relying on the defense giving him open shots. That's a different dynamic and a different type of player. The closest we have is Bogey, and if you can afford to have a couple of those guys (especially when the rotation spot you're upgrading is Niang), then that's a huge boon.
In terms of role, he played 16 mpg last year with Milwaukee and 20 mpg the year before with us. Niang is currently picking up 12 mpg and that would essentially be where I'd see his average sitting. Clearly he's familiar with the other guys and the system, even if it's a bit different. It would not require a huge adjustment period. All the things that Niang is currently doing well that we're not wanting to discount, are all boxes that Korver can check. I do think this is one of those moves that has a lot of arrows pointing to why it would make sense with little cost in terms of adjustment/chemistry or other issues. And you can still keep Niang on the team.