Focusing on the category display:
For forums that have a flat category structure, and distinct category colors, this might be fine. I have a few reservations about this, however:
- It’s slightly more difficult for new users to learn the structure of the forum. While not a huge concern, it is something to consider.
- On forums with category trees (sub-categories), the colored bar won’t be able to display the color structure. For some, this is preferred information. For others, it’s just noise anyway.
- How does this work with a pinned topic? Since pinned topics display a chunk of the OP beneath the title, how will this work in that scenario?
Otherwise, taking into account other changes that are in the pipeline, I think it’s pretty good. The one thing that might be worth considering is including the OP’s avatar next to their user name, but that might make that area too busy. As I said, worth considering.