I like this statement a lot and particularly approve of the prominent inclusion of “joy,” because even in wiki software, good design does more than just provide maximum utility. But I think there is one subtle but important thing missing here.
In addition to making things useful and beautiful, good design is a form of communication. In particular, design communicates values, attitudes, and a sense of the intended audience. Is your company edgy and exclusive? Boring and bureaucratic? Aimed at the mainstream, or at the elite? Wordlessly, design communicates these things.
So for me, the thing that's missing here is our values. And it actually goes beyond just communicating them. Values are part of the process, because when we make decisions, we frequently work to align users' immediate requests with our understanding of the movement's highest goals. This can be a tricky area to talk about, but if a Statement of Purpose is intended to help guide and explain decisions, then it might be worth including some reference to this. E.g.:
“Our goal is to ensure that Wikimedia products and communications follow a design process that's centered on the user and guided by our movement's highest values and goals. Based on research to understand people’s needs and motivations, we explore solutions that meet those needs and express our common aspirations.”