At the moment, the Cardinals are meeting with Seahawks offensive coordinator Darrell Bevell at the team's facility in Tempe. It was widely reported this morning that Arizona was trying to set up a interview with Arians.
Arians was a finalist for the Bears job, a position that he really wanted, but it was given to Marc Trestman. As the Colts offensive coordinator, Arians has a good gig with having Andrew Luck as his quarterback and lots of young pieces on offense, so there is no guarantee that would leave if offered the Cardinals job.
If Arians is hired, Ray Horton could be out as Arizona's defensive coordinator. ArizonaSports.com released a story which said Horton wouldn't be retained because Arians has promised the defensive coordinator job to Todd Bowles wherever he goes. Bowles was the Eagles DC this past season.
This news would upset a large portion of the fan base because many want Horton as the Cardinals next head coach. Even though it could hurt things in the short term, it might be best in the long term in order to begin the rebuilding process that needs to be done if the Cardinals want to get back to the top of the NFC West.
As of right now, all of this is all pure speculation. Arians could be the guy and Horton could be out. Only time will tell.