Sitting in the middle of the car, in the middle of the train, has always been preferable for general riders, "squishable" cars or not. In a train-on-train collision or grade crossing collision with something very big, most of the energy is absorbed by wrecking or derailing the first car or locomotive. And sitting in the middle of the car generally produces a more comfortable ride. Works on light rail as well as real trains. It's also why, in survivable airplane crashes, the folks in the back seats are more likely to be able to get off.

CEM equipment "squishes" at the ends, outside the main passenger seating area. Yes, if the main doors are on the ends that can be problematic for egress, but most modern passenger cars don't have them there. The main body of the car still has to meet basic crush requirements. Same thing with your car: the passenger section is built very strongly, to resist crush and rollover, but the ends are sacrificial and the engine is usually designed to dive under the car if pushed back toward the passengers.

There are, of course, situations where somebody hits the train some distance from the ends (see: truck hitting Amtrak in Nevada, or SUV hitting the door of your Corolla). Sitting in the middle won't help much if that's where they hit. That's a low-percentage occurrence for trains.

Speed doesn't kill. Stopping very quickly against something hard or pointy does. If you sit facing backward you're far less likely to faceplant on something hard when thrown out of your seat by a sudden stop. Facing backward, the worst damage is likely to be a whiplash, or maybe catching the forward-facing passenger across from you with your teeth. CEM reduces the peak acceleration on the passengers, so the hits on each other and interior parts are more survivable.

I do have to wonder, though, whether as with automobiles the use of CEM will increase long-term costs (as well as initial purchase). It doesn't take much of a hit with an auto to get into the crash-absorbing structure, and it's very expensive to repair correctly. With your car, that usually results in the insurance totalling it and selling it for parts and scrap. While appropriate for something with a depreciated value in the low $10Ks, railroad cars (and Ferraris) are another matter.