Well, GF is a company that aims on making more and more profit. If they feel DLC would sell I don't see why they shouldn't do it... Look at Pokemon Bank! And as always they would say: "for providing better customer satisfaction" and blah blah blah... Masahiro Sakurai (Creator and Director of the Super Smash Bros Series) openly said "Smash 4 will have NO DLC" but after a while EVERYTHING on Smash 4 is DLC. They can't just exclude the beloved Battle Frontier for no serious reason.
What kind of excuse is: "We feared that People wouldn't use the BF, so we decided against it." Yeah, right... Like BF wouldn't be the best place for VGC competitors to train. Or OLD school fans would finally get a new BF after years and years of waiting the ORAS sequel... So, they analysed people's opinions and exactly like Mewtwo they will bring it back as DLC. OR as a new feature for Pokemon Z, which I believe will be a crossover between regions. (possibly Hoehn and Kalos)
If they intended to do DLC, they would have programmed the games in a way that makes it easy for them to do DLC, but they didn't, because they are comfy with their current model of bringing out final products and then moving onto the next project (which sometimes uses a previous project as the basis, making the new product an upgraded version of the previous, which makes DLC unnecessary and less profitable than not bothering to do any DLC). That's their mindset on DLC and if it's gonna change, it's at least not going to be before this generation is finished, so DLC plays no role RIGHT NOW.
As for the Battle Frontier....now this is going far off-topic, but I'll explain it one more time as careful as possible.
They didn't "exclude" it. They didn't ADD it, big difference. A full-blown Battle Frontier is not a small feat to add into a Pokemon game.
Think back through the franchise. We have seen 2 Battle Frontiers so far. What kind of games did GF get around to making them? Emerald and Platinum, both projects where they started with a previous product as the basis. In both cases 90% of the game was already THERE, which opens up a lot of development time for very specific features that are otherwise out of the question due to the core game having priority. It is in the third version/sequel-games that they shift their focus from "satisfying the casual audience" to an engaging post-game, a good polish and features for the more serious and advanced players.
ORAS was not that. It was about experiencing Hoenn and its story again. Which means they had to remake the whole region and story from scratch, add enough new twists to keep things interesting, create more mega evolutions, add features like the dexNav and Soaring, reintroduce contests and secret bases and most importantly, they figured they had to give us something simple but quantitative to do for the longer wait till the next games: the biggest amount of legendaries to collect in any Pokemon game to date (which also neatly closes up any loose ties to previous generations and absolves XY-sequels of that job so they can focus on whatever they want then).
If you honestly expected a Battle Frontier in ORAS, then sorry, but your expectations were simply not anywhere near realistic. To me and people I discussed it with, it was obvious they would not attempt to tackle a big post-game feature like that in basic games like these. The attempt at making Rayquaza relevant in the post-game too had priority, and the Delta episode is all they managed to pull off (certainly less elegant than Emerald was at tidying up the actual plot).
ORAS had certain goals (revisiting Hoenn and its story, expanding both and connecting them to the current theme of Mega-evolution. Target: nostalgia-prone and casual players/collectors), and a BF was never meant to be a part of that because everything else was priority for this project and it didn't fit into the development cycle, if it was considered at all (because there is a good chance they planned to make one in XY-sequels the whole time already anyway)
But hey, as if it wasn't reassuring enough that the odds for a Battle Frontier or something similar are actually realistic for the XY-sequels by default, no, we can even be completely certain that there will be, due to ORASes Battle Resort flat out telling us in the face "Battle Frontier is in development", which is a clear hint for one being included in the games that come next.
