Nokia needs a phone between the 920 and 820 as well as a WP8 700 series phone
Not many manufacturers are making WP8 phones and Nokia would be wise to releasea few more WP8 devices in the next few months to flesh out the WP8 lineup for different proce points and features.
IMO the WP8 Lumia lineup should consist of:
920 - $499
910 - $399 (4.5 inch HD screen, 16 GB storage, SD card, non pureview 8MP camera)
820 - $299
720 - $199 (4 inch WVGA, 8 GB, SD card, 5 MP)
Then the 600 and 500 series can be based on WP 7.8 and be even cheaper.
I personally would buy the imaginary 910 I've described above in a flash...