Well, I'm all for a biodegradable coffin. That's because, a fair amount of me will be all biodegraded, after.
It took me awhile to get to this thread. I have been in a fairly good mood today, a feeling of accomplishment setting in. I didn't want to hurry on to set ... as in finished and in concrete.
I dislike that idea of a vault - unless ... But, you know, try as we might, biodegrading will occur.
Ashes to ashes, dust to dust ...
Baskets might be okay but coffins should be easily formed out of dust and ashes. They wouldn't have to be of any organic origin.
When I was a kid, I used to enjoy finding a block of pumice, we called it pummy stone. I'd chuck it in the Rogue and watch it float, downriver.
Pummy, uh, pumice is volcanic ash, more or less.
Huh? Float off

. Metaphorically. Keep the remains out of water - at least until that ashes and dust coffin serves its purpose with cremation or a few centuries of burial.
Steve