If it's not a successor to the 780 Ti (15 SMX), then it's likely a Titan Successor (14 SMX), or a 780 successor (12 SMX). Using the Maxwell Model, a 15 SMX Successor would likely have 25 SMMs and 5 GPCs. What gets tricky is the ROPs, as we haven't seen a multi-GPC Maxwell - yet. I believe they are scaling it directly with the GM107. This would give 16 ROPs, 2MB L2 Cache, and 128-bit memory per GPC Disable 1 SMM and you have:
5 GPCs
24 SMMs
10MB L2 Cache
3072 Shader Cores
192 Texture Units
80 ROPs
640-Bit Memory Bus
6GB GDDR5 RAM
If it's a GTX 780 successor, disable 1 GPC:
4 GPCs
20 SMMs
8MB L2 Cache
2560 Shader Cores
160 Texture Units
64 ROPs
512-Bit Memory Bus
3GB GDDR5 RAM
I personally would love this. But if we're throwing out rumors, then here's a rumor via logic.