So basically a mobile hotspot with a webrtc webpage on which your headset microphone gets relayed? Participants can scan the QR-Code to join the hotspot WLAN and get directly redirected to the webrtc session
Seriously though, I think it's an under-explored area. Several years ago[^] I thought it could be a fun way to do an ephemeral social networking type thing on the tube; then something a bit similar ('YikYak'?) became briefly popular (in the UK at least) but just using GPS or whatever for location, still with a central server.
I think there's plenty of interesting things you could do ephemerally, P2P over Bluetooth or mobile WLAN.
([^] edit: that's not some weird claim to fame, I mean it in the sense of I've long thought this should be good, but then, I've not bothered to do anything about it, and neither it seems has anybody else, so...)
It's the implicit derision, that eg Twitter is inherently worthless because I could glue a few libraries together to a database over a weekend, and have a simplistic system where users who are able to broadcast short messages to other users, that is so odious about the "build it in a weekend" mindset. It denigrates the very real, but largely invisible effort it takes to scale a system up to that level. For any of us who have been involved with scaling a system up, it's invalidating to have your work invalidated like that. A Twitter or Dropbox clone built in 48 hours isn't going to handle the scale of actual Dropbox, nor will it be as resilient as actual Twitter in the face of eg a whole AWS region going down.
Build something awesome this weekend! (or even just something useful; it doesn't even have to be software) Just don't shit on someone else's hard work, even (especially!) if you don't get it. That Dropbox, reduced to it's basics is "just" a filesync client, and isn't actually the most technology fascinating project when described at that level, is an reflection of the oversimplification of the problem at hand, and not the inherent worthiness of solving that problem. The social aspects of what a program can be used for goes wholly underestimated and misunderstood a lot of the time. No one could deny the effect on the world that Twitter has had (though we don't have to agree on if the net effect was positive or negative), but many people still don't see the value of a product that isn't a revolutionary new technical product, like terabit wifi, but that's a reflection on their lack of imagination on their part, and not a poor reflection on Twitter as a business idea.
Then you could package it with a "creation studio" to create your own version for tourguides, museums, etc. Resell some hardware also as per requirements. You've got yourself a nice little business that seems useful for the business and client.