No goal is the very nature of sandbox though. I think the problem here lies with permadeath as well - people are gonna try to avoid it no matter what. Making a permadeath game "hard" to play is not a good idea. Let's consider Dark Souls as a hard game - sure you lose something upon death, but if you had to go from start every time you died people would just give up - I know I would. Same goes for every hard/competitive game - you keep practicing/dying until you're good, but you don't really lose much progress (if any) when you die, so you can keep repeating.
I don't see how this game could be made harder and not frustrating at the same time. I could imagine random events happening like bug infection on your crops that you would have to heal, but I can also see this becoming just another chore to handle over time...