Reframing from Camera roll now works properly, thankfully. The next big update to Nokia Camera will probably be as part of the Nokia Black roll-out, with teased improvements in image quality due to tighter integration of the Windows Phone OS with the Lumia 1020's camera hardware.
From Camera roll, you can now successfully tap on the 'Nokia Camera' link to open up the image...
...and then reframe to your heart's content, safe in the knowledge that the changes will be properly saved.
Anyway, go grab Nokia Camera here now, it works on the Lumia 1020, 925 and 920.