It is just a suggestion, and it probably won't be implemented, but a few Legendary Pokemon are known to have Genders. An example would be Latios and Latias. In some of the movies and episodes, there is proof that some Legendaries can have young. An example of this would be Pokemon Heros where they explain that Latios' and Latias' father died saving the city. One episode for an example has a mother Lugia and her baby. So, why not make a few legendaries be able to breed?
then they wont be legendary anymore, as you stated above, sure lugia had a baby, but that makes the entire species consist of only 2 which fits the legendary status, Now imagine if lugia was breedable, you'd see everybody with a lugia in the anime just like any other pokemon, it woulnd't be legendary anymore.
The reason legendary pokemon can't breed in the games is to keep their legendary status and not to be able to produce as many as you want of them, but not because they are genderless,
and btw, ditto and a handful of other pokemon are genderless but they can still breed in the game.
