Yes, this is absolutely true. Once i had an idea to implement HWNAT for the C7 router.
- Documentation is very limited.
- There are some leaked sources and its a full mess - many kernel modules are patched, some changes looks weird, etc.
- In this sources some chipset limitations are mentioned, like number of such hw fastpath channels. Moreover - it is very clear that it wont work correctly with nf_ infrastructure, so potentially is a huge security risk.
So after all it was decided no to do anything like that in OpenWRT and just to suggest some modern CPU boards for anyone who needs recent speeds.