I'm seeing some conflicts between the test findings and the conclusions.
All these sound like issues with over rotation, possibly made worse if the seat is not braced. The other issue seems to be direct contact with the head, that could happen regardless of bracing the seat as the dummies ramp up the seat back.
Their main conclusion is about energy absorbing padding in the infant seat. I'm not seeing how such padding is going to help at all when the issue is the direct dummy head contact from ramping and striking part of the vehicle interior, like a vehicle seat back, center console, pillar, etc. It should help for the back of the dummy head, though. Besides, I'm not sure if they've looked at current infant seats, but many of them do have energy absorbing foam around the head.
Anyway, I do agree with one thing, something I have been saying for some time. Head excursion is critical and likely to be more important in terms of serious injury than other measures. As for rear-facing seats, we really need standards updated not only for the testing they describe with a front seat back, but also to allow for things like foot props that would help resolve the rotation-related injury.
I'm not sure how their advice on LATCH is likely to help. They didn't describe the dynamic at all. In fact, a European routed shoulder belt that goes behind the back of a rear-facing seat could actually be a benefit for the injury mechanism they discuss. Of course, rear-facing seats that allow this type of routing are not very common in the USA.