I don’t know the details of the honda system, but I do believe they are taking a different approach for their 50 state system. By the time this is done (and the rules keep changing) there will probably be lots of different versions proposed (I have no idea what the domestics are doing). I’m sure the EPA will be concerned about the potential that customers’ will fail to have urea systems refilled at the required interval. I don’t know how the “non-urea” system compares in terms of cost/fuel efficiency/etc. I also assume that verifying that these systems are functional will become part of state emissions tests (where they exist for diesels). I also do not know where they both are in the certification process. It will be interesting.
Personally, I’ll just keep driving my old diesel.