Yeah, using Plan 9 for the graphics rendering stuff Hollywood was using Irix and NeXTSTEP for, wasn't never on the team's roadmap, specially when on Inferno the UI was based on Tk.
Cinematic graphics rendering has nothing to do with UIs and the technologies used there.
Plan9 provides no performance issues or technological barriers to doing e.g. ray-tracing or scene previews for graphics work. Even with respect to displaying it in a UI.
