Elon Musk's Tantalizing Tesla Tweet: What Could 'D' Be?

Tesla CEO Elon Musk tweeted Wednesday night about something called "D," which will be officially unveiled October 9.

The photo that accompanied the tweet was of a partially opened garage door, with what looks a lot like a Tesla Model S peeking out. Everything was in black. Mysterious!

Musk also said that in addition to "D," Tesla will pull the cover off "something else."

So what's coming from the electric-car startup, which could actually use some good news as its stock has declined over the past several weeks (it was down almost 20% from a trading peak of $291 on Sept. 4 - but it's on the rise Thursday morning)?

An All-Wheel-Drive Version of the Model S

This is almost certainly what's in Tesla's Black Garage. An AWD version of the Model S has been rumored since the beginning of the year, and now that the company's Fremont, Calif., factory has been retooled to build the Model X SUV (arriving next year), the technology is in place to construct an AWD Model S. All-wheel-drive is an important variant in luxury cars - AWD offers more stable driving dynamics than rear-wheel-drive and is obviously better in bad weather. The Model S is currently available only with rear-wheel drive, tricky in the snow, and Tesla isn't invested in only selling cars in sunny California.

The Model X will come what what Tesla has labeled a "dual motor" AWD system, so that's where the "D" comes in. This was my guess when I spotted Musk's tweet, and speculation has been widespread on the Internet that's "D" indeed means "dual." Explanation: The Model S "D" will need two electric motors, one for the front wheels and one for the back.

High-Performance Model S?

The existing Model S is already pretty snappy, but it's also pitched at buyers who love tech, love the Tesla story, and love the planet - more than they love going very fast in a straight line or around corners. The skunkworks nature of the photo in the tweet suggests that Tesla could be starting its own high-performance division, maybe aimed at racing. Mercedes has AMG, BMW has M Sport, Audi has S models. This is something that Tesla lacks and that would add a bit of dash to the company's story. And there's now a new electric-car racing series, Formula E. Presto, Elon Musk becomes Silicon Valley's Enzo Ferrari - on the weekends!

My money is on this one!

It's a Diesel

Hahaha! But seriously, maybe Tesla has decided to deal with "range anxiety" by incorporating a diesel-electric hybrid engine into its designs, perhaps as a result of the company's relationship with Daimler (Germans love diesels!). Of course, a diesel-hybrid Model S - or any diesel-hybrid Tesla - would run 100% counter to what the company stands for: 100% all-electric transportation.

Autoblog's Noah Joseph also suggests this possibility.

It's the SpaceX Mars Rover

Okay, probably not.

It's A Model S That Runs Entirely On D Batteries

This is Tesla's new battery-swapping plan. It will take several days to replace the Model S's existing lithium-ion battery pack with perhaps thousands of D batteries, but D batteries are pretty easy to find and you don't need to build a $5-billion Gigafactory to get them.

It Stands For "Debt"

Tesla doesn't currently have its own finance arm - if you want to to take out a loan to buy a Model S, you have to go through Wells Fargo or US Bank. I once asked Musk if Tesla was interested in becoming its own bank at some point - which makes sense if Tesla matures as a carmaker, given that it can make a lot of money through what's called "captive financing," especially if it can sell directly to the consumer at its stores - but he scoffed at the idea. That was a couple of years ago, however.

Convertible?

This theory is making the rounds as well. But it would imply that there will be a coupe version of the Model S, as well. Not a crazy idea. But some of this stuff is limited by the fact that Tesla doesn't really have enough production lines to build numerous variants of its cars.

An Updated Roadster

The Roadster was Tesla's first car, with components supplied by Lotus (although not, according to what Tesla's called a "myth," entirely by Lotus). It would be kind of good if Tesla could keep the Roadster going in some form, simply to have a sportier model in the lineup. But then again, the Roadster was more of a means to and end, and a sexy proof-of-concept for Tesla's electric-car business model.

Driverless Tesla?

Musk has said that all Tesla's will have self-driving capability in a few years, so maybe. But it doesn't really fit with the whole "black garage" thing.

What about the "something else?"

I'm guessing it's a smartwatch.