To me, the Battle Frontier is the most entertaining form of endgame content to date in a Pokémon game. Sure, you don’t get experience for your fights, but that puts all the more emphasis on sportsmanship and competition. You can win some pretty awesome and useful items, too, and even face off against pre-configured player teams in later-generation offerings.
For the remakes, I’m hoping the Battle Frontier will be taken online, and expanded to something like a multiplayer Olympic Games of Pokémon. X and Y’s online experience was impressively robust, and merging it with what the Frontier has to offer could literally add hundreds of hours of replay value to the upcoming games. If players can create events and offer up specific rare items as rewards, or set custom parameters and rules, that number would increase even further. Unfortunately, there’s no guarantee the frontier will be included, as the Frontier was part of Pokémon Emerald, not Ruby and Sapphire. Still, past remakes have included the third version of a generation (HeartGold and SoulSilver had Crystal content, for example), so I’m hoping Game Freak does the right thing and includes an awesome, modernized Battle Frontier for players to check out.