This youtube video is of the commissioning runs 7 Dec 17. The interesting thing to look for is the "bogies" under the coaches, they are an articulated type nothing unusual although not used in the UK▸ except Eurostar 373. Its still usual to see twin axel bogies supporting the 2 carriage's, however if you look at the youtube video you will notice a single axel supporting 2 carriages.
The initial reports did say the carriages were made by Talgo, so the use of what is their signature design feature isn't a surprise. They are longer than the original Spansih ones, though.
The initial reports indicate excessive speed some 50 mph over the limit as the cause, I do wonder if the single axel contributed to the magnitude of the derailment also the fact there was a 120 ton plus locomotive attached to the rear.
I am sure the USA TSB will look to see if the above added to the accident
The fixed structural pivots of the articulated bogie (even with one axle) should hold the carriages upright much better than any coupling, though once the train concertinas that effect no longer operates over the full length of the train.
The analysis after the "Polmont Cow" didn't support the idea that having a light trailer at the front made derailment easier, let alone that having mass at the rear would. I think the key point is whether and where the train concertinas, and that is due to the back overrunning the front. Once the lead carriages are running off the track they must slow down fast, probably much faster even than brakes can on the track. I suspect the mass of half a train pushing a carriage, when its front end is being pushed back and sideways by the half that's derailed and now slowing, would be enough to produce this kind of opposite-side derailment.
After the Polmont Cow accident (I was living in Bo'ness, which is very close, in 1984) my thought was that having a heavy lead vehicle, which would decelerate slower than the trailers behind it, would be a good idea. That ought to pull the derailed part of the consist straight and so resist it concertaing, which at Polmont the leading
DVT‡ clearly didn't.