Microsoft today aounced that they are releasing Windows 10 Insider Preview Build 14291 build to the list of devices that will be capable of receiving updates as part of the Windows Insider Program except the Lumia 635. Microsoft is plaing to release this build for the Lumia 635 at a later date.
Going forward – these devices can receive new builds from our Development Branch that we release to the Fast and Slow rings. As we stated previously, only devices which are eligible to receive the Windows 10 Mobile upgrade will be able to get preview builds from the Development Branch.