Report of a user enabling BLE (--enable-features=WebAuthenticationBle) 

"Whats interesting though is that I did see the UI pop up the first few times and then an hour later I got a segmentation fault. The only way to get rid of the segementation fault was to nuke  the Library/Application Support/Google/Chrome Canary folder. Even since then, I can't get the ui to pop up, though chrome still communicates to the authenticator behind the scenes."