I don't see what advantage this has over snailmail to themselves?

I think the most likely nefarious thing is the question of intentionally blocking aliveness checks. If the Satoshi heir waited for his keys from this what element would he spend a few million interfering with to get his inheritance early?

That's a human issue not a technology issue. There's nothing technology can and should be programmed to even try to deal with, unless probing user's brain for intent is on the table...