I understand that Spotify won't allow you to change the username as it is used in internal stuffs of Spotify, but how about adding a Display Name field to user's account settings that by default is the same as username and it's not used for anything else but to search the user and display it's name. That way, the user users can change it as they like ?
Updated on 2020-03-12
Thanks for coming to the Community, and adding your vote to this idea.
You can now add or change your display name!
A display name replaces the username where it shows on your profile, app, playlists, and Friend Activity.
There's more on this here, and here.