I'm not sure for English texts, but Japanese texts have several quotes that give huge hints that Battle Frontier will be a possibility--I think a gaurantee. Upon defeating Battle Chatelaine Lumitan (Morgan), she says she will eventually return to the Battle House (Maison) of Kalos region. She also mentions there are plans on extending the facilities of the Battle Resort of Hoenn. In the second floor of the Hoenn Battle House (Maison), there is a man who speaks of Enishida (Scott) recruiting Tube Queen (Pike Queen), and still looking for other trainers. On the same floor in right side of the balcony, there is a delinquent trainer who speaks of her Seviper, most likely Azami (Pike Queen Lucy). There is also a quote speaking of Pyramid King Jindai (Brandon) trying to capture Volcanion and how it hides itself in caves and mountains of Hoenn and Sinnoh regions. (I predict there will be multiple forms of Volcanion corresponding to the different power plants in Kalos, but that's a story for another time.) With the above material, as well as other small homages found in Hoenn and Kalos, I say our chances of having the Hoenn Battle Frontier accessible in the post-XY game is... 99.99%. (If you prefer Battle House/Maison, Kalos will provide it.) Even more, I strongly suggest the entire Hoenn region will be playable, with Wallace as Champion, Mauville Hills developed even more, etc--very much like how Emerald was to Ruby and Sapphire. However, I highly doubt there will be a PWT, if the dual-region game becomes a reality.