Nope, it was common in 8 and 16 bit home computers, and in respect to PCs themselves graphics memory was mapped into the main memory until the arrival of 3D dedicated cards.
And even with 3D, integrated GPUs have existed for years.
The CPUs with iGPUs didn't also have the memory on-chip. The Nintendo 64 did. Not sure about the old home computers, but I thought those had separate memory usually.
Of course not, because they are not designed as SOCs, the only
memory on chip is cache, it doesn't change the fact the memory is one whole block shared between CPU and iGPU.
And even with 3D, integrated GPUs have existed for years.