Access control - allow specified number of devices

Setting access control stops credentials being shared by subscribers, but also prevents more than one device being accessed by a single user. Deciding to have it on or off is probably a compromise either way. I'd like to prevent credential sharing, but I am mindful that a many people use more than one device and my guess for most of those its a desktop and a mobile device, i.e. two devices. Would it be possible to be able to have a finer setting for access control to allow for 1, 2, and infinite number of devices? Or even a variable number?