People use this tag way too freely, for example:
http://pokemondb.net/pokebase/210351/is-round-a-suitable-alternative-for-hyper-voice - literally nothing to do with XY, accept for the said Salamence being in it http://pokemondb.net/pokebase/210176/why-do-people-hack-pokemon - people have been hacking Pokemon well before X/Y were released. http://pokemondb.net/pokebase/209800/im-confused-with-pokemon-roles - competitve roles existed before XY.
Do these questions really need the "xy" tag? i just want to know what qualifies for an "xy" question before retagging it.
Any question with the X/Y tag means this question's answer's information must be true to gen 6, so yeah, this is a legit tag.