When it comes to Hackaday | Belgrade Conference badge, it has some interesting features which can be exploited for fun and profit:

• IR port for bi-directional short-range communication
• nice-looking, bright LED display
• Unique ID accessible from user-space code

They also have well-documented open-source hardware and software with a lot of example code. As well as embedded kernel and USB bootloader for pure hacking pleasure. All of this makes this badges great for this project, but I believe this idea can be expanded to other platforms and means of communications.

More details here: https://hackaday.io/project/9509-badge-for-hackaday-belgrade-conference.