Lightning?
Everything is a speculation at this early stage and PPRUNE being just a rumour network, since “aircraft was airborne, according to some reports, for 11 minutes and crash site, according to the latest news, is only 6 miles away” is it possible that a “massive lightning strike” blew all lights, radios and EFIS out and the crew was trying to come back to land in total darkness, no radio or Nav and IMC?
Could have a lightning strike affected ELT too?