Shannon is being promoted to Associate Head Coach, which apparently means he'll be something of Bielema's #2 man on staff, and he'll likely get a nice raise, but he is apparently not going to be the Razorbacks' defensive coordinator.
Since it's been several weeks since Ash left, there had been rumors that an unusual provision in Shannon's buyout with Miami prohibited him from taking the job until February 1st, but that appears not to be the case. Or if it is, it doesn't matter.
If Shannon is happy with this set-up, I think it's a good situation for Arkansas. The last month established Shannon as a huge recruiting presence in South Florida, particularly after Charlie Partridge left. At least in theory, not having to worry about the added responsibilities of being a coordinator will give him more time to visit and recruit the region.
As for the defensive coordinator, the latest rumor is Robb Smith, the former defensive coordinator for the Tampa Bay Buccaneers in 2013 and at Rutgers before that. You may remember him as the coordinator who gave up 300+ receiving yards to Cobi Hamilton even though he had three NFL draft picks in his secondary that night. But that was just one game. I'm sure it was an off night.