If a server is needed anyway, could it be implemented in easier, OpenWRT-compatible way?
You and many others :) WebRTC (Web Real-Time Communications) is faux-P2P, in that in order to establish the P2P connection, you'll need a server in-between as browsers cannot accept incoming connections, you can only dial out and then start listen for replies.
> If a server is needed anyway, could it be implemented in easier, OpenWRT-compatible way?
I'm not sure why it would have to be OpenWRT-compatible? OpenWRT is just Linux run on less-powerful hardware (over-simplification obviously), so anything Linux can run, should be able to run on OpenWRT. Find your favorite STUN/signalling server and try running on OpenWRT, should work fine.
It uses WebTorrent trackers and is easier to setup offline on network.