The interesting thing is, in the EU version of TTYD (or at least the Spanish one, which is what I've played), Vivian is kept the same as in the Japanese version. Why NA version got changed in that regard? Who the hell knows the real explanation.
While I've only played the English version and know of the Japanese version I think we have to look at Vivian's sex. The only thing it matters for is Vivian used as a joke with her other two sisters in their group. In the Japanese version the group was the Shadow Sisters with the joke being Vivian is messing it up by not actually being a girl. Now the English version went for something like the Shadow Sirens with Vivian messing it up by not being evil enough. I see that as a convenient comedy change and while it's true who knows the real explanation that is a plausible scenario.
At least it isn't an inconsequential change that bites them in ass ala Capcom with Street Fighter (though that was more not having M. Tyson suing them with the bite being possible confusion about characters unless terms like claw, boxer and dictator are used) and Ace Attorney (it's set in America, in the future with the bites being all these small things like Japanese shrines, film camera as evidence in a case taking place in 2014, left handed drive car).
Assuming Nintendo is handling this, I don't think they'd do that - have they ever straight-up cut out content just to save money on VA/translation?
Fire Emblem Radiant Dawn in the Japanese version playing on hard difficulty had more dialogue. Rather than use this as the base as for the US translation they used the normal difficulty instead resulting in less text.
Weirdly though I think the chapter narration and previews were added for the localisation (as well some other features like game able to run in 16:9 and some gameplay tweaks) so you cut costs on text but add costs with narration.
But if you want to save money wouldn't you just leave those extra scenes unvoiced instead of cutting them out? People can read...
The whole want to save money part of this rubs me the wrong way. It feels like the only reward for Braverly Default being a success is Braverly Second got a low budget localisation. I'd hope outselling Lightning Returns (at least NPD numbers said that) would be enough to earn it's stars. Then again maybe 2016 3DS market doesn't warrant having large sums of money thrown about it and there is also the Japanese performance of the game to consider so maybe I'm wrong to think to think this.
On the other hand maybe the Japanese reacted poorly to the multiple outcomes for sidequests and the need to play the game umpteen times to 100% the cutscene viewers.