I'm starting to think that AMD is sticking with VEGA on the 7nm APUs for footprint reasons. From what I'm reading, the equivalent number of NAVI/RDNA CUs would consume a non-trivial amount more die area than the existing VEGA cores do. Given how tight AMD is on wafer capacity at the moment, I don't see them wanting to put any more die area towards the iGPU than they absolutely have to.
If Cezanne can bring the increased core capabilities of Zen3 and the increased effective cache performance of the unified 8 core CCX, and provide another 10% clock speed uplift on the Vega CUs, it will still be a worthy generational upgrade to Renoir. Now, will it be better than Tigerlake 4C in mobile? I don't know. Obviously, it'll have a core count advantage. It'll have a tweaked process. Tigerlake should rectify a lot of what was wrong with Ice Lake, meaning more Mhz and lower power draw. It'll also have a further improved iGPU. It'll bring with it Intel's noted advantages when it comes to extracting performance and low latency from their memory controllers as well. By that point, I would hope that AMD is specifying DDR4-3600 for their mobile platform, and maybe faster LPDDR4X for those types of systems, to help deal with the greater memory demands of a faster iGPU.
Either way, I still see the biggest loser here being Nvidia as they continue to loose volume on their MX lines of dGPUs. I suspect that, as Renoir has made everything from the MX330 on down completely irrelevant, and bumps up against the MX350 (which is essentially a low power 1050 mobile), we'll see Cezanne do the same for the MX350 as well, and start to push slightly into low power, cut down mobile 1650 territory. Look at the current laptop market. Whereas a few years ago, Mobile 1050 laptops were commanding prices at $900+, you can get 4GB 1650s in the under $700 category now.
As AMD and Intel improve their mobile iGPU products, and memory technology also moves along, there's less and less of a demand for the volume/Low end mobile dGPU products. Nvidia is going to have to do some more innovation in that area to keep their volumes up in that market.