Honestly an idea I've had with the recent surge of interest in LLMs is some type of robotic pet. I feel like LLMs can understand human language and images(hopefully soon) to the extent that a pet should be able to. Some kind of robotic dog that can not only express emotions, but understand what you say to it, seems like it would be pretty successful if done correctly.

The nice thing is that it doesn't even have to understand perfectly, a GPT-4 level of vision/language understanding would be perfectly fine. It doesn't have to hold a conversation, just be able to be happy or sad when it should.