There was a recent project I was working on where I was going to be using a Cisco 3850 switch as a wireless controller, which is a fully supported feature that is build into this new line of switches. The big difference here is that you must have all access points connected directly to the switch acting as the controller (or agent). This is different than a standard Cisco Wireless controller where the AP’s can be connected to other switches on the network with all communication relayed back. There are also things called wireless agents as well. Long story short, these are also wireless controllers, but the big difference is that they pull their licensing info from another source -> a regular 3850 wireless controller. The idea here is you would have multiple wireless controllers on your network, but only have to manage licensing on one of them. The downfall here though is that all wireless networks and other settings have to be managed on each individual controller or agent. This information will not be shared between the devices. That being said, should one of the agent devices go down, the controller in the group does not pick up those AP’s either, all controllers and agents are separate when it comes to normal operations.
The lab I was working on had a 3850 acting as an agent. It was connected to another 3850 that acted as the backbone. The goal was to have one single controller interface that could manage wlan’s for the entire building. It seems that is not possible and wireless networks will have to be managed on each controller unless another product, like Prime, is used.