As I have spent some time and money on this I would like to chime in.
In DP1 & 2, whether you got the handoff option was based on having APPLE USB 4.0. (Had to be Apple part)
Since DP3 & DP4 it now requires the loading of WiFi AC kext. Doesnt actually require wifi AC, just that the kext loads. You can have no BT at all and still get the Handoff option in preferences.
Basically, Apple moved the goalposts. Much easier to add USB based BT then to add WiFi AC. We will be offering Apple based USB dongles next week on our website but they are no longer the whole answer.
2 guys named nicklad and manic harmonic have figured out how to hack the kext to load on older machines. You now have to put a boot arg to keep your machine in dev mode to run hacked kexts. (Thanks big brother for watching out for me and protecting me from myself !)
If you have a machine that can accept the updated 94360 cards you stand best chance of using those features but final results will be determined by Apple. By using parts from newer machines you stand a better chance of avoiding the obstacles Apple seems intent on putting in our path