I’m not against the idea, but I do think it’s a bit unfair. There are dozens of projects KDE relies on that never even get the chance to ask for donations this way, simply because they don’t need a GUI.
I believe KDE should at least offer to share the donations with other projects, projects that would otherwise have no voice. Something like the old Humble Bundle donation method would work really well, and let users to choose how their money is allocated.