The 680, 670, 660 are believed by many to have originally been targeted as nVidia mid range lineup...... and the "big kepler" (BK) is already waiting in the wings. But given the cards competitive positioning in the marketplace, nVidia has no reason to release BK at this time.
What they eventually call them is anybody's guess....again assuming those pundits are right.. While to my eye, their reasoning was sound, only time will tell
The GK110 gaming chip will be released to counter the AMD 8970, likely near the end of this year in time for the holiday buying season. With 670's, 680's, and soon 660 Ti's selling like hotcakes, there is no reason to release anything more powerful.