I like Model Viewer. Being able to keep it running while designing is a BIG plus. I don't like the lack of a full set of visual styles but I'm sure you're working on that.
What I would like to see added would make Corridor editing more efficient. You could add station display signs that pop up along any baseline for which you enable it. These would not be labels, as they would disappear when you exit Model Viewer. The advantage is that now you can visually see where you need to zoom in order to see the detail you want.
I imagine the display items as little signs that stand vertically above the baselines but you could also do it the same way as InfraWorks.
