I fear AI primarily for this because I see it as an enabling technology for brain simulation, but I also see cryogenic preservation similarly in that it removes the time constraints from the rate of progress - at least from the individual's perspective.
Who knows, some weirdo hyper-libertarian future civilisation could decide to take these "dead" people and simulate them to act as NPCs in their new horror game. The fact there is a non zero chance of being revived into some hellish existence like this makes me terrified of cryogenic preservation.
When I die I want to be sure I'm dead. I want matter in my body to be brought to the highest state of entropy reasonably possible. I understand not wanting to die, but personally when I die I'd prefer to die knowing it will be over.