My thinking is router manufacturers will probably not do this. Because if you don't have a firewall and expose all your computers to the Internet via IPv6, Everything Just Works (assuming the rest of the world uses IPv6, which will be a close approximation to the truth in the future world we're talking about). Which means those insecure routers will have a better user experience for the vast majority people in the market, who don't have a clue about networking and would rather gouge their eyes out than learn about it.
Routers currently don't do this for IPv4 for a good and simple reason: When you're assigned a single public IP by your ISP, there's no way to automagically tell which host is supposed to receive an inbound connection.
The "good" news (from a security standpoint) is that the most clueless will probably be using IPv4 for a long time to come, helped along in their foot-dragging by the eventual release of IPv4 space by early adopters of IPv6-only.