XY has about as much post game as Diamond and Pearl. I like XY for its gorgeous graphics and Pokemon, specialty features like mega evolution, pokemon rides and playing with your teammates in Poke Amie, but neither DP or XY are the postgame heavy installments in the franchise. If post game is really what you want the most then the games for you might actually be Black 2/ White2 or Heart Gold Soul Silver, which have gigantic post game :)
While XY does not have the contest hall unfortunately, it does have a few things to do that Diamond and Pearl do not have. There are 3 places that you can battle all you want post game, the Battle Chateau where you hold a noble title and rise through the ranks fighting lords and ladies and can issue writ of challenge. Next there is a high roller's restaurant in Lumiose City where you wager frightening amounts of money on your battles starting at 500,000! But the most well-known of the three would be the Battle Maison, which offers you single battles, doubles, triples, rotation battles and challenges you to keep long, unbroken winning streaks of 20 or 50 battles in a row of each format and eventually engage in boss fights with Chatelaines. In the Battle Maison trainers fight in a manner that resembles competitive play somewhat and will have Pokemon equipped with useful items like choice scarf or life orb. At the higher levels they will use legendary Pokemon against you.
What I enjoy most about Xy post game is a story about Looker from the Sinnoh where his character gets a lot of development. Post game you can become a detective with him. He will train you to look for clues, you will fight crime all over town and there are some emotional scenes that involve looker and a young woman that I will not give away.
If you like the contests then you are in luck with Pokemon Alpha Sapphire. It brings the Battle Maison back and the contest halls. The contests have been revamped with beautiful new graphics and 3d animations. Your Pokemon's portraits will be painted and hang in the Lilycove museum if you make it through the master ranks. In addition to the standard ribbons you will unlock a magic ribbon that will float around your Pokemon when it enters battle if it attains master rank in every category. There is also an event Pikachu that dons adorable cosplay costumes you will receive for competing in the contests. You can even unlock beautiful furniture for your secret base, mega stones and be awarded healing items and pokeblock berries by your fans and meet a fun new character Lysa who is the biggest star of the contest world and your opponent at the highest contest levels.
The secret base is a house you can build in Hoenn in a variety of places. You can collect furniture, dolls, artwork etc to make it feel like home and even turn it into a gym and have battles with others once you exchange codes.
Some of the best story content in Oras also begins post game. There is a dramatic new plotline known as the Delta episode where an apocalyptic chain of events that was not in the original Ruby Sapphire games will unfold, and an adventurous new character named Zinnia is at the center of it all. There will also be lots of legendary Pokemon from past gens to track down and catch through places called miragespots too. So that was enough for me at least!
