Oh, I kind of forgot about that. That would indicate some kind of target but I'm not sure that level of fidelity would be feasible for anything but a high budget console game. Especially with switchable costumes.
Also IIRC VisualWorks were credited with the AR stuff. Not sure quite how that stuff works from a rendering stand point.
Well, I guess I'll boil down a little comparison for the heck of it.
For promotional reasons, Square Enix released a bunch of screenshots of Bravely Default rendered at 800x480 resolution, which gives us a sense of what the game would look like as-is on a higher resolution system with the same art assets. As you can see below (I've included four images), sometimes it looks quite nice, while others it looks decidedly insufficient. It would be a lower to lower-mid end game on a system like the Vita and probably distinctly lower end on the 4DS.
For comparison, here is what the AR models look likel. While I wouldn't expect it to look exactly like this (the Edea model is decidedly less detailed than Agnes for example), I wouldn't be surprised to see these types of proportions and art style in a 4DS Bravely Default game, since it matches up to the concept art design and they put them on the cart. Sadly no one took a picture of Ringabel, so I tried to make that one manually. Given what games like Digimon look like, I think you could do something similar on Vita hardware.
Now, here's a game on September 2014 mobile hardware by Square Enix. If we assume the 4DS's hardware is only two years old by the time it launches in Fall 2016 (at the earliest), in theory you could get something like this at a lower resolution. It's possible the hardware is notably older than this, but I'd still expect something marginally above the Vita. Obviously the art style would be rather different, but I'm using this as an example of feasible levels of detail.
So yeah, overall I feel that there would very plausibly be at least a moderate budget increase. Even if they didn't shift art styles as I'm proposing, the environmental detail in the first batch of screenshots would likely increase quite a bit as well as the detailing in the chibi character models and potentially everyone's animations and particle effects.