The rumour is based on the idea that since 7nm node affords accommodation of more cores, it is a Vega 15 iGPU is likely. While it is difficult to be certain a proper memory implementation could see them further widening the gap with the Iris Plus Graphics G7 and the NVIDIA GeForce MX250.
AMD should be launching the Ryzen 4000 'Renoir' Zen 2 APUs sometime in November and the new APUs will be out at CES 2020, but there is a steady stream of leaks about Vega iGPU has been trickling down steadily. The latest info we are seeing is that a Vega 12 (and possibly Vega 15) iGPU are happening
Leakster Komachi on Twitter who has identified several Renoir listings with B12 in the classification indicating a 12 CU (Compute Units) iGPU. This makes sense because the 7nm process can allow for more cores to be accommodated on the die.
Another punter Locuza thinks While Vega 12 is possible a Vega 13 or even a Vega 15 configuration is also possible. If the Vega 13 exists it could have a 3+3+3+3+1 CU configuration with eachCU cluster getting 32 KB L1 instruction cache (L$) and 16 KB K$ (constant cache) or a more probable 3+3+3+2+2 config. A Vega 15 could have a 3+3+3+3+3 configuration.
7nm Renoir APUs means that AMD will continue to use Vega and reserve Navi iGPUs for Zen 2+ This is because AMD cannot tape out 7nm Navi in time for Zen 2 Renoir.
Renoir APUs could further widen the performance gap with the Intel Ice Lake Iris Plus G7 and also eclipse the NVIDIA GeForce MX250, but that depends a lot on the memory implementation and the available bandwidth.