Honestly, it looks to me like Masuda worded the answer poorly (not to mention the interview is translated) while also missing the point of the question.
First off, it was clear there wouldn't be a BF in these games way ahead of release. Just the absence of any mention whatsoever in the marketing was a huge clue. Especially considering that it's a feature big enough that it was the main thing they were showing off leading up to Emeralds release, but even moreso considering they had no problem whatsoever in spoilering the Delta Episode for no reason.
And secondly, a big feature like the Battle Frontier is not just something small they can slap onto a game a week before it's out (or when people go so far as to say they've "taken it out" ^^" this is worse than the customisation whining). It requires investing a decent amount of development time into it, and simply looking back, just remember at what points in the past they got around to making a battle frontier so far:
-Emerald
-Platinum
Notice what those have in common?
The basis for them was a full pre-existing game at the start of development. In neither of those 2 projects did they have to create a game from scratch. They merely modified and improved, so of course the development time will go into something bigger for a core audience rather than the casuals.
In ORAS, they had their hands full with remaking the whole Hoenn region and story from scratch, bringing it up to date with 3 generations of improvements, keeping up with the standard we're used to atm, adding new designs, AND even decided to add a bunch of really cool features like Soaring and the DexNav. For just a year after XY, they did a tremendous job (on the other hand, they work on more projects simultaneously for a few past gens already anyway, but then the business standpoint kicks in, ala how much more development is worth putting in for how much predicted additional profit. And we all know ORAS sales would have been marginaly different with however much more content they'd have put into these game. So any extra development is of better use for whatever the next game is)
And that brings me to my point: it wasn't because they don't care about non-casuals anymore ever, it was simply a matter of priorities and time constraints.)
They're always alternating on the subejcts of nostalgia vs fresh, casuals vs core-fans, evolutions vs standalone region etc..
I'm fairly confident we will see the Battle Frontier reinvented in the Kalos sequel, if not earlier (whether that's a Delta Emerald with unexpected twists to justify it, or as an e-shop exclusive pokebank compatible game based on ORAS like the demo we had or who knows what).
Gamefreak have a habit of being awfully unprepared and missing the point in interviews, especially when they're not being interviewed in japanese..