when I put an "R View (Workspace)" node without connections into a Metanode, then the Metanode gets reset after each execution. That's especially stopping any loop that contains that metanode. You can convince that loop to execute step by step, though.
Additionally, when I use a variable containing only a filename to set the path of an "Image Port Writer" node, it complains that the folder didn't exist. If this behaviour is intentional, there should be a better error message, I think.
Edit: one more feature request: could you please enable SVG output for R nodes with image ports? That would be great!