Ripping a page from the Apple rumor trolls, we now know Tesla Motors applied for the Trademark on the "Model E" as of August 5, 2013 according to filings with the US Patent and Trademark Office. It makes sense when you give it some thought. The Model S is the Sedan, the Model X is the Cross-Over, so it stands to reason the Model E is the Economy model or maybe even Everybody's Model. Perhaps instead of having a giant touchscreen, it'll have more of an iPad Mini sized screen.
This is the actual JPEG Tesla filed along with the name. It specifies no specific font or size in case you wondered.