but unclear if who will pay for any legal - criminal complaints defense.
Boeing is on record as providing legal defense and financial protections to their "Authorized Representatives" (ARs) if they are sued for their actions as an AR (provided they acted in good faith).
I doubt there are many engineers who would be willing to act as DERs/ARs if they could be held personally liable - I certainly wouldn't have. The nightmare scenario of your system causing a fatal crash is bad enough. Knowing that such a nightmare could also result in financial ruin for you and your family - why would anyone be willing to do that? It's not like ARs get any extra pay in return for their responsibilities...