If you are referring the demo as the trailers shown with double battles previewed, then I must add that those were all Wi-Fi challenges shown. There haven't been any in-game double battles previewed to be within the game as yet. The twinsin the demo were in-game evidence of double battles.
However, with the new reference of the idea, and the implentation to it since RSE, then I have no doubt Double Battles will be brought into the in-game play of both Johto and Kanto. There are many different locations in which they can be implied on, but a few might be with Soul against Team Rocket, and possible Lance as well.
Stating everyone likes or enjoys double battles is an understatement, as it isn't always true. There are many major Pokémon players who prefer the original single battles over the double battles. What a pointless effort to enflate your own ego, he was expressing his feelings and although what he said cannot be proved, can you name me three people onthe community who totally dislike double battles?
With confirmation from recent trailers, double battles will be brought to Wi-Fi as it was in DPPt. That is no surprise seeing as the fourth generation games, including HeartGold and SoulSilver, all run on the same frame of the way things are planned out to play.
As for Lance, it is a possibility. However, as for a double battle with or against Giovanni, that couldn't be said as yet noting how Giovanni never appeared in the original Gold, Silver, or Crystal games. True. However it would be awsome if the new or prolonged Kanto storyine involved Giovanni.