I completely understand the direction you're going with enhancing the QDP view. I like using QDPs when doing data grooming or reviewing One of the challenges, however, is that templates aren't available in QDP view, and we are heavily using templates via the Rich Text Template Sharing lab. We're rolling this out across a very large organization, and using templates on portfolio items to drive consistency in the item descriptions. If a portfolio item is created in QDP the default template is not applied, so users either need to switch to full view before creating or switch after creating and manually apply the template.
My gut tells me that even if this weren't the case, when adding the kind of detail we're putting into a portfolio item (sort of a light business case) a user would want to have more real estate for the description than what is available in QDP. I like the convenience of seeing details of one item while still in the context of my list, but would like to see the same editor in both places.
I will add that for the most part I really do like where you're taking Agile Central.