Indeed, putting the old clues together with his new hints narrows it done quite precisely.

It will be a Ground Effect lifting body on an electromagnetic rail. The lift is provided by aerodynamic effects, and thrust is provided by electromagnetic force.

Based on the details of the design, it would be capable of supersonic speeds like the Concord, while employing Ground Effect like an air hockey table, and propelled like a Rail Gun.

The biggest challenges will be keeping the vehicle stable and at a constant distance from the power rail at high speeds, as aerodynamic disturbances can destabilize the vehicle. Given Elon's expertise with rockets, this should not be too difficult.

EDIT:

An prototype of a ground effect train:

http://www.youtube.com/watch?v=EaOnrIRf_Mg

Elon's will use electromagnetic propulsion instead of electric fans.

EDIT 2: I just realized this may be Elon's electric jet idea. He may use a ram-air electric jet at high speeds, and only use the power rail to get the vehicle to supersonic speeds where the ram-air engines are most efficient. This would make it MUCH cheaper than maglev by eliminating the power rail on the majority of the track.

EDIT 3: Rail gun diagram.

http://www.howstuffworks.com/rail-gun1.htm

The walls of the guideway will likely house the propulsion system.

Half serious, half tongue-in-cheek, but he's apparently had this idea since at least Iron Man 2: http://www.youtube.com/watch?v=EuG2AVFB-g0

Musk has said that his idea of the hyperloop involves a system that "can never crash". Assuming that he's not just talking about really robust safety protocols and instead is referring to some inherent property of the system I think there's probably some missing detail here.

Although I think overall this is probably pretty close.

I believe it will be encapsulated like a dedicated guideway train with walls on both sides so that a de-rail is impossible. The failure mode would likely be the craft slowing down and landing on the track if power is lost. As a result the vehicle can never crash, but simply lands on the track as it slows down.

I believe Elon is referring to aircraft failure modes when he says "crash", as his Hyperloop vehicle won't drop from an altitude high enough to ever hurt the vehicle or passengers.

EDIT - Response to InclinedPlane's comment below:

The vehicle's angle of attack will be kept almost constant with aerodynamic control systems, similar to a rocket. The reason why NASCAR and F1 cars have spectacular lift crashes is because they are not allowed to have active control surfaces, allowing small aerodynamic perturbations to evolve into massive ones.

The vehicle will likely be kept a few meters off the track to allow for these perturbations. Since the angle of attack is controlled, the only way the lifting body can stall is if it is suddenly immersed in a continuous stream of fully turbulent air. Although extremely unlikely, this is possible, so it can be mitigated with an encapsulated tunnel with fans blowing air in from the outside to gaurantee consistent laminar flow, similar to a wind tunnel.

Maybe, but I'm not convinced. It doesn't matter if you're flying or not, if you're traveling at supersonic speeds and you run into anything, even if you hit the ground from a height of 10cm, it's going to be a bad time. Also, if you're traveling that fast it is magnificently easy to gain a dangerous amount of altitude quickly just by having your vehicle rotate and hit a favorable angle of attack. Just look at how dangerous and dramatic crashes in formula 1 or nascar are, and those vehicles are on the ground, and traveling at maybe 1/5th as fast as a hyperloop vehicle would (and with 1/25th as much kinetic energy).

I'm convinced there either must be some other factor at play or Musk must have worded his statements stronger than is warranted.

Exactly my bet, also if the rail is a tube he gains a way to store electricity in a kind of condenser, has an easy way to keep the "train" stabilized and also isolates the sonic shock from braking half the windows between L.A. And SF. Of course on top of the tube it's easy to install some solar panels.

I take that to suggest it will be affixed to the track, sort of like roller coasters, unlike a traditional train which simply sits on the tracks.

http://images3.wikia.nocookie.net/__cb20120420164756/coaster...

The soviet Ekranoplan is another cool vehicle that makes use of ground effect: http://en.m.wikipedia.org/wiki/Lun_class_ekranoplan

If the track is not evacuated, what happens to the supersonic shock wave off the nose of the train? Seems to me it would reflect off the ground and enclosing walls, causing all sorts of turbulence.

This is exactly what I'm trying to figure out at the moment. My guess is that the walls will be just far enough to allow the reflections to not disrupt the air immediately surrounding the vehicle, and/or there will be gaps, allowing the shocks to dissipate into the surrounding air.

I assume that a non-evacuated tunnel would require air moving at a speed that is close to (or the same as) that of the train. Keep the air circulating constantly, so it's sealed but not evacuated.

I've thought about it and I believe this is the most likely solution. The vehicle would remain aerodynamically subsonic, but could attain supersonic speeds as the air in the tunnel speeds up. This would also allow vehicles to follow one another without too much separation. Turbo fans can be used to keep the air moving throughout the loop. If enough vehicles are running at full speed, the system will always be "pressurized" as the vehicles themselves will accelerate the air in the loop.

Passenger/cargo loading would occur outside the loop (a fork) and would be brought up to speed by the power rail and inserted into the loop.

EDIT - It appears jacquesmattheij agrees with us:

http://jacquesmattheij.com/elon-musk-and-the-hyperloop

That would explain the "loop" part of the name.

But where could he actually build such a long, and presumably straight, railway? He said the system has no "right of way" issues.

I've seen some proposals of building a train in the median of the interestate, a raised track. However, even the interstate isn't straight enough for hypersonic travel in most places, so dunno. I think 'bullet' train speeds in the 200mph realm might be feasible on existing right of ways doing that, but not sure how the hypersonic vehicle would work.

The Nullabor plain in Australia?

Wishful thinking from a Perthite sigh

That would be a very cool way to traverse Australia. Do most travelers circumnavigate Australia to get to the other side? I've seen some videos of the "road trains" hauling six trailers across Australia.

Best guess? the ocean...

I don't have a source, but I have seen him mention in a talk or on twitter that "right of way" would not be an issue. [citation needed]