This is a good idea. In fact, I've seen data scientists propose something similar. But if you develop the technology to be able to talk to your dead relative, why only allow people to use it at the grave site? After all, it will be basically a chatbot that sounds like the dead person. You could create a computer animation that looks like the dead person, and it would be far cheaper and easier than building a robot. Plus, an animation wouldn't ever run out of batteries (which is going to be a problem because it's expensive to get enough geothermal energy).

All you'd need is the writings and videos of the deceased. This would allow an LLM to be able to talk in their style, and generate content with their knowledge and opinions in mind. As a result, a dead person could be around to chat to their descendants, funded only by occasionally pausing to tell them about the end of financial year sale on Casper mattresses.

Imagine if we could have been raised by our ancestors, not just our parents! We would have centuries of accumulated wisdom to guide us! And the first thing we'd do is conclude "It's all gone downhill since we stopped burning witches!", and then off we'd go to invade France for the glory of the king.