Honestly i'd go 2.5" from cat back for now with a traditional muffler at the back, running the header with cats would not be a big deal, all in a days work at any exhaust shop, one guy on here cut off the midpipe flange from the OBX one and welded it onto his stock midpipe. There's more gains to be had with no cats if you have a header (or an improved manifold, whatever you want to call it), but if you have regular e-tests it's not very convenient and probably not worth any gains.
Luckily for me my license and registration is registered to a countryside address, where the Drive Clean program is exempt, so until i get rid of the car i can do whatever i want. The cops don't care either, the only time i could see them looking under the car for cats is when you were driving like an idiot or are otherwise being a dick to them.
When i just had straight pipe i got pulled over for noise, and assuming he was going to ask about cats, i said that it still had cats on it. He didn't care, he said that was part of the emissions system and all he cares about is noise level... which was funny to me since he should also be enforcing emissions compliance, but whatever.
As far as aftermarket goes, you can theoretically get anything you want made up for a Versa if you want, it's just usually not cost effective, simple economics rules. The more market interest there is, the wider the cost of R&D can be spread out over multiple buyers. I could get an aluminum performance intake manifold made for my MR18 by a local performance/fabrication shop, but i'd be bearing all the R&D costs unless i could get people on here or in the area to commit to buying in. Plus usually the first product prototype made is the least efficient and most costly, which is always the case with anything. It's like how you're not very good at something the first time, like painting a car, but the more you do the more efficient and higher quality the work becomes.
