It has been hinted that Irelia's brother Zelos is possibly being made into a champion and is currently in development.
Irelia, has among the highest potential tenacity stat in the game, capped at 64.9% (40% from her passive, granted at least 3 enemy champions are within her sights, 15% from the Tenacious mastery and 35% from any tenacity item in the game, i.e. Mercury's Treads after being calculated with diminishing returns). Thus, the duration of almost all crowd control effects in the game can be cut by more than half against Irelia.
Previously, Zac could achieve 86.18% tenacity, the highest, while using Let's Bounce!, Tenacious and 35% from tenacity items in-game. However, this only lasts for the duration of Let's Bounce! and so Irelia's is more reliable. This is no longer possible after the tenacity boost from Zac's ultimate is removed.
Irelia is the focus of a LoL meme "better nerf Irelia", in which Morello determines that a certain champion is currently overpowered, but chooses instead to nerf Irelia, due to his numerous alterations to her skillset.
Irelia received nerfs one day before her release because Morello said she was too "annoying to play against."
ricklessabandon stated that Irelia is somewhat similar to a lich, and her weapon acts as her phylactery. 
The naming of her style, "Hiten Style", her backstory, and Xypherous' confirmation show Irelia is based on Kenshin Himura of Rurouni Kenshin. 
Her French jokes are references to the character of Brice de Nice from the eponymous French film.
Her joke "My blade is not only precise, but totally gnarly" references that she rides her weapon like a surfboard and "gnarly" being a term used by most surfers to tell if something is cool or good.