You know, IPv6 was supposed to be deployed in a fashion very similar to what you proposed. 6to4 was developed to create automatic tunnels between site border routers, and ISATAP was developed to create automatic tunnels within sites, safely behind the protection of the site's firewall/NAT. The intent was that vendors would enable these technologies by default, thus allowing IPv6 to be used with no assistance from network administrators or the core IPv4 Internet.
But this didn't happen. IPv4 and NAT worked just fine, so customers didn't want IPv6, and vendors didn't implement it.
I see no reason to believe your proposed solution wouldn't have met the same fate. You can't force vendors to implement something that nobody wants or needs.