Well there's a few consoles out there that have unified memory and CPU/GPU on the same chip ;)
Actually Intel PCs are already in this category too...
You benefit from not having to waste time physically moving data between two different RAM locations, and you can flexibly just increase how much video memory you have by stealing it from system memory :)
Anything where you dynamically generate data using the CPU per frame will benefit, as you don't have to stream it over the PCIe bus.
Of course, you need high performance system memory though, otherwise you're shackling the GPU -- e.g. existing intel systems have DDR3, but using GDDR5 would be awesome.
The problem with GPU to system memory transfers isn't interface or memory speeds, it's the huge pipeline stall that they require.
Which is exactly why a true shared memory architecture would be great. You could actually use fine-grained algorithms as no data would need to be transferred, simply a pointer/handle here or there.
I assume he's talking about the fact that the GPU usually has 1+ frame of latency, so the CPU must wait before reading the data (else it will stall). That disadvantage doesn't change, but yes, transfers would be eliminated. There's still complications on top of just having a pointer -- e.g. knowing when/which caches to flush/invalidate/wait for, to ensure coherency. But that's something that current APIs do for you :)