Is this for a BSc undergrad thesis? Honestly, most of those, just pick something vague and kind of interesting. Don't worry about "has already been explored in great detail": that's to be expected at the BSc level. About two months in, you'll decide your original plan was stupid and you need to do something totally different, which is why the "vague" part of your proposal is so important. I've seen people just do like "a mobile educational game" or "a programming language" or "a search engine" for their BSc project. As long as you're halfway competent, you (or more likely your supervisor) will find a way to stick something unique or novel into it. It doesn't have to be Guernica, just a demonstration of your abilities.
If it's a MSc dissertation, a lot of those are just "I read a paper that had a really good idea and then decided to implement it because nobody else implemented it yet". Or, if you're more theory based, "I read and paper and decided to extend it a little bit because nobody else has done that yet". Has your friend been doing a literature survey?
If it's a PhD dissertation, your friend is fucked and should probably not be doing a PhD.
Sorry, that wasn't clear at all! I'll edit the post in a minute. It's just a BSC dissertation, so I guess not much is expected. The idea of a game, e.g. mobile game sounds appealing, especially for him, I think his main issue is the whole "has to have little research in the chosen field". Thank you for your help :)