It's been requested since the old client, and its something that would make the usage of the client more convinient.
For people that doesnt have a top tier computer, but even for a pretty decent computer, after closing the client, a few minutes of waiting is required before you can launch it again, otherwise it freezes. For me it happens a lot when im acting impatient. But yeah for the beloved Pro players and Streamers with their Pro computers its not a problem.
But like, its not even hard to make. People complain about and ask for things that would take a lot, for example a completely new team of programers and such, but this is a simple job for the Client Developers. Just creating a shortcut for logging in, or even switch between saved accounts, and when it happens, the clent can relaunch. Sometimes, when I wanna log into another accout, by the time I get to logging in, I forget which account I wanted to log in, and then accidentally logging into another accoutn, and then I can start over. Lot of inconvinience. And dont tell me Riot is not aware of this issue, or not aware of the fact that most players have 2-3 accounts.
And for people that are against having multiple accounts, I can tell you that I have a lot of friends in a lot of different ranks. I always have an account under lvl 30, and I have one in very low elo so that I can play with my friends, and its not smurfing because my highest rank account is Plat, the lowest is Silver 1, and I only play Solo Que on one account.
So just make it so that we dont have to close and relaunch Client every time we wanna switch accounts. It takes a lot of time and there could be a much easier way if you cared about actualy community requests and not just drawing Lux skins to jerk off to.