When Elon Musk burst onto the scene in his little Tesla Roadster , it seemed a matter of time before electricity rendered gas-powered sports cars obsolete. It hasn’t worked out that way. Automakers have struggled to bring purely electric two-seaters to market. The ones that managed to emerge have been flatly rejected by consumers. Porsche has walked back plans for an all-electric lineup of Boxster and Cayman models, seemingly spooked by technical hurdles and tepid response from its fanatical