While I agree with you, having a globaly routable address doesn't help you if you can't accept incoming tcp/udp connections.
My ISP blocks such connections on LTE mobile network. Maybe so you don't pay a lot of money for traffic if people DoS you? It doesn't make sense, since ICMP ping packets are allowed.
Well, it's either my ISP or the android phone I have. Does android have any firewalls enabled by default?
The problem is NAT as it makes it impossible to directly address, and NAT doesn’t exist in IPv6 (because NAT is primarily needed to workaround limited public addresses).
IPv6 support is pretty 'widespread' at this point. >50% last I did a quick test
You unfortunately need ubiquitus IPv6 support to actually rely on IPv6, which isn't going to happen anytime soon.
So you really need to consider the benefits of dual stack v4 and v6 simultaneously within the same group of players. Might be useful, but it adds a whole heap of complexity.
One could abuse BitTorrent's existing DHT infrastructure (: