I've now read all of Android's preview site for testing out Android O; it is unclear to me, though, how to test out the Bluetooth 5.0 functionality in any environment. The Downloads page lists only a few devices that can be flashed with preview images, but none of the devices listed (Pixel, Nexus models) have Bluetooth 5.0.
My question is, how can we have a chance to test out Bluetooth 5.0 before Android O makes its debut? Or will that particular feature set not be available during the preview? I am unable to find any information on this throughout the Preview site nor in the listed developer resources.
As of May 2017, the only Bluetooth 5 capable device is the Samsung Galaxy S8 with the Qualcomm Snapdragon 835. Some of the features of Bluetooth 5 do require an update to Android O (specifically Bluetooth low energy advertising payloads) but others like range and speed improvement don't. However, you will most likely also need a Bluetooth 5 enabled peripheral to fully take advantage of the new improvements.