I pdb-stepped into the ledger-specific code, and initialization fails with
ModuleNotFoundError: No module named 'btchip'           
Of course - because, I installed btchip for python2, but electrum 3.x uses python3 
Follow this advice: https://www.reddit.com/r/Electrum/comments/7a9o30/electrum_30_is_here/dp8dfyk/