Do you prefer 1 main column layout (Iris) or 2 main columns (Jumble)?
It's convenient to keep the main feed open while opening profiles and threads on the right. Most of all, you don't need to care about remounting the feed on back nav and keeping scroll position.
But it can be a bit more hectic and overwhelming feel, harder to focus. Maybe it could be a configurable option. Either way, Iris could use the right column more efficiently; maybe have configurable widgets that you can add and remove. You can now also toggle the right column off if you don't want it.