Sounds interesting, especially if we promote the content type editor to the menu on the left:
1. It's optional, as the content types feature doesn't have to be on by default
2. I spend a lot of time in there and it's bugging me to have to go through Content
3. Once you've done that, it frees the tab real estate for that categorization.
Alternatively, we could have filters like we do in the feature list or in the contents list. Now that I mention it, having live filtering like in the feature list would be easy and great.