That sounds ominous. The way I read that is not only DP's won't be available but tuning itself wouldn't be allowed. This could destroy the aftermarket companies. Anything that the EPA says could alter emissions.
AFAIK, Cobb has skirted this by not disabling any O2 readiness monitor. It only deactivates illuminating the light for certain CEL codes. So, the CEL is still stored and you will not pass an emissions test. Since the secondary O2 is still enabled and monitoring, EQT recommends disconnecting it, since they've seen the tendency to run rich over time from the rear O2 trying to change things. This seems to be a Cobb only issue, which could point to them being the only company who isn't bypassing the secondary O2.
I don't know what other tuning companies are doing to avoid the CEL with the secondary O2, but on my previous vehicle, tunes could force readiness and it was possible to pass smog tests w/o needing to swap downpipes.
If the EPA is that serious about it I wouldn't want to risk making DP's in my garage and then selling them to someone who fails emissions and is traced back to the builder. Until all states do visual inspections and actual sniffer tests I would guess if you can pass emissions you would be okay.
@GTI Jake do you have any input on this?
It's going to be harder for homebrew downpipe makers as well, since companies like Vibrant are pulling their cats off the market as well.