There was a thread somewhere discussing this (or something along the same lines).
The D7100 is the logical naming convention (D3000/3100/3200, D5000/5100/5200), but it would put the 'D7100' out of line with the current Dx200 naming.
So will Nikon just skip the D7100 and call it the D7200 instead, thereby making their current line up all Dx200s, or will the replacement break the trend?