I posted this one year ago and still no one comment.
We really need this! Because extended properties is only one thing that you can't manage via interface, only via import csv. Please think about this — it will really help us to keep our catalog clean.
Now I can manage my «Item Extended Properties» only from export/import. It's not useful.
I need a separate page for managing all extended properties that I have.
1. It can be the same screen like «Categories».
2. Also I need to see all linked products to this extended properties. At least qty of it. But more useful - when clicked on a qty I can see a list of all linked products.
3. I need to link/move all products from «extended-property1» to «extended-property2».
Look at the screenshots.