Some ideas are tarpit ideas until enough people get stuck.

Location estimation (figuring out where you are) based on indoor WiFi / BLE is one example. Compared to 15 years ago, we have (IIRC - I don't work in this space) super-precise timing API from the modem, and there has been work on the reflections issue (the two big problematic things that non-RF people typically miss).

What about multipath? Is that not an issue at wifi wavelengths? Or is that a sub or superset of reflections? It was quite a long time ago now that the first "proof" that one could use leaky WiFi to "see through walls" and observe people moving around inside a building from without.

Participate in a transmitter hunt (also called a foxhunt or a t-hunt) where the organizers or the people hiding the transmitter know their stuff. Reflections and multipath can lead you miles away from a transmitter location.

Anyhow, someone asked me if I knew how to do this without consent once; that is, if I knew how to track people in a building without them knowing. This was 8 years ago or so. I had hoped saying "that's not possible" would dissuade them, but instead they just never spoke to me again.

I did a project on this in like 2010 as a student hobby project. It wasn't accurate, but I also had no idea what I was doing. I mostly did it in a naive way, where I mapped out signal strengths in various rooms (it was dorm floor, 2 rooms shared each) and then trying to figure out where I was based on it. As a non-CS student I thought it was cool......

I think there is a difference between ideas that are based on a fundamental misunderstanding of how the world works and ideas that we do not currently have the capabilities to solve.