Contemporary painting has many surprising components as well: I know painters who use rabbit-skin glue[1] to prime or gesso their canvases. Heavy metals and raw hydrocarbons are also pretty common.
(This isn't to imply that grinding up a human being into paint is okay.)
i bet there are a lot of people that would enjoy being turned into paint and 'living on' in some art.
with more and more people ditching traditional religious burial rites, there's probably a lot of potential to come up with new things to do with the dead
True, there was extensive effort, but wasn't the effort geared towards providing the deceased god a path back to the heavens or wherever they had come from?
So, presumably after they had ascended with the help of the burial provisions, the remainder of the body was irrelevant?
But perhaps this part was not clearly defined in the teachings.
I don't think so. Consider the effort to hide tombs full of gold and jewels. If the humidification was just a temporary expedient, wouldn't it make sense to loot the tombs once the soul had passed on, as a general policy?
I think they expected to be bodily resurrected at some future date. I think a lot of people today expect to be bodily resurrected at some future date.
Regarding consent, I wonder about the ethics in general of "studying" ancient Egypt. It's almost like an arbitrary line in the sand that once it's old enough, it's okay to unearth the dead and study their lives. But clearly we would unanimously reject the idea of people digging up our grandparents to study them. Probably the same for 19th century decedents. Probably the same for the bodies of those in the Renaissance period. But somewhere between that and ancient Egypt (and surrounding areas) we deem it okay to pilfer their memorials.
When is consent of the deceased really required in modern contexts?
For example, the remains of Salvador Dali were exhumed in 2017 because someone claimed to have been his biological child entitled to some of his estate. Not only did Dali not consent to this, but parties (including a foundation associated with him) pointed out that testing against other parties could have ruled out the possibility of Dali being the biological father.
The line in the sand is generally when someone's recent enough to have living people object, the more loudly they'd object the deeper the line.
Funnily enough, a lot of contemporary spiritual groups do claim some memetic ancestry from Egypt, though I don't think that extends to the bodies of people from that era in most instances.
(This isn't to imply that grinding up a human being into paint is okay.)
[1]: https://en.wikipedia.org/wiki/Rabbit-skin_glue