Riot Games have slowed new champion releases long ago since the champion pool was growing too quickly. In order to keep things fresh, champion reworks now happen more often. The latest addition to the rework list is Akali.
League of Legends had 40 champions back in October 2009 when the game was first released. Riot then started adding new champions every two weeks or so, which later became one champion per month - but the champion pool was still growing too fast. We will be getting the League's newest addition, Kai'Sa, when patch 8.5 hits the live servers and she will be 141st member of the roster.
These days, release dates vary from one to four months between new releases and we get champion reworks in the meantime to keep things interesting. The latest addition here was Akali, the Fist of Shadow. I'm not kidding, that is her actual title.
Riot's champion update schedule got updated itself today, putting Akali on the list. As of right now, the list only states that besides Akali, there are also Aatrox due for gameplay update and Irelia, in for both visual and gameplay update. It is implied that Irelia's rework will come first, as this has been an active topic for months now but the exact dates of each update are unknown for the moment.
These updates don't have a set interval on which they occur, and on the bottom of the page you can see that Evelynn and Xin Zhao received their cosmetic enhancements along with new abilities within two weeks of each other. The wait for the next one was four months, when Swain received his tratment and became Lucius Malfoy lookalike.
While Akali's kit did prove troublesome to balance out and needs a rework, her visuals aren't that outdated compared to the likes of Amumu and Mordekaiser. The reddit post about the rework contains some interesting information as well, such as the fact it's CertainlyT that's doing the rework.
Please Riot, don't let him make another Zoe.