Bug:
Using betterendforge-1.16.4-1.4.1(.jar), I have noticed that crashed ship chests do not generate any loot; instead they generate random empty chests.

Potential cause:
From reading the source (more specifically StructureHelper.erodeIntense() and subsequent methods), I have noticed that none of these methods seem to account for any stored NBT (such as loot tables).

Misc:
I am not sure if this is directly related to this bug, but from looking at CrashedShipFeature#addStructureData(), the code specifically ignores entities such as the item frames containing elytra. Is this a(n additional) bug, or is this an intended behaviour?

So, since i follow what the Fabric developers do, i can say for sure that loot in chests hasn't been implemented yet, but it will. About elytras i can make a guess and say that their absence from crashed ships is intentional. That would really make too easy to obtain elytras in my opinion.

Logically speaking, if your ship crashed and you had the option to literally fly so you weren't stranded, you would probably take the elytra.