But design is a different beast. Collaborative design of complex systems has a few stages. There's a rapid prototyping stage where 3 people in a room bouncing ideas off of each other and scribbling is better than anything else I've done. Then you circle back with a document that formalizes things (like an RFC). The second part can be done with a distributed group. But the first part is better when people are close to each other. You see this even in distributed groups like OSS projects. They have conferences and work sprints where the maintainers can be colocated for a bit and brainstorm about things in person.