OKC had a ridiculous amount of picks coming there way from the PG-13 and Westbrook trades. They probably have little interest in the #10 in a so-so draft. They will likely cash in on Chris Paul this offseason and that leaves them with Shai and Schroeder as their main guards, possibly moving Schroeder back into the starting 5 but he'll still be a solid 6th man for them and a veteran presence on a young team. Sure, Kelly would add some of the veteran presence also but I can't see him resigning in OKC and I would think OKC would want to see if he'd resign there before trading for him also.
Giving up Kelly and the #10 for a Sixth man like Schroeder who sucked in Atlanta before finding a home in OKC recently is an overpay, plus he's also expiring and isn't likely to be a good replacement for Rubio in 2 years either, if he's retained beyond his current deal.
They should be able to find a Sixth Man like Jordan Clarkson for the MLE, if they're interested in signing someone outright. He can score, facilitate, and defend. Plus he's used to coming off the bench in a role of instant offense and playing point. He's a true combo guard in skill and size, while Schroeder is too small to play much SG unless you had a PG with Shai's size to pair him with.
If the Suns wanted to trade for someone on an expiring deal, I'd like to see them talk with the Nets for Spencer Dinwiddie. Oubre for him, straight up. Resign him and he could take over for Rubio as starter either in Rubio's last year or when he's expired. His game is more complete than Schroeder, offensively and defensively, and he's got a lot more size at 6'5" 215 pounds.