A monolithic 8 core Zen die is TINY. It won't be very big even with a more capable GPU than found in the 3400G, look at the 4800H in mobile! There's some rumor mill speculation that APUs will form the low to upper mid range of the stack for the 4000 series, thats up to and including something like a 4800G (rather than X)...
For OEMs it'd be a win/win. No need for a dGPU to add to cost/complexity. Smaller cases, simpler cooling, more than 4 cores. I've always been bemused by mainstream Ryzen NOT having a basic iGPU
A Ryzen 4800G desktop would be all kinds of awesome.