It not being used on PC has absolutely nothing to do with how good or useful it would be. It isn't used on PC, no doubt because of what it would add to manufacturing complexity, transistor count and cost.
The EDRAM in the Xbox 360, for example, provided more than just extra bandwidth. It allowed some developers to get away with using less external memory bandwidth than would have otherwise been required without it. ESRAM on the Xbox One, thanks to its close proximity to the execution units of the GPU, no matter how many times people try to deny it, will help the Xbox One in a similar way. It will help with more than simply just giving the system some extra memory bandwidth. It will help reduce the bandwidth cost of most post processing algorithms. In fact, with fast enough on chip memory, they can become completely free of external memory bandwidth.
http://beyond3d.com/showpost.php?p=1738762&postcount=3325
And, for the record, this isn't a stupid vs post. It's simply to showcase, with added evidence from an actual game developer, that the "all you're getting from esram is extra mem bandwidth" argument is false. Who cares what's used on the PC. We are talking about what's used on consoles, and how that may benefit the consoles. The if it was any good, it would be used on the PC argument is the weakest possible argument anyone could even attempt to bring into this discussion. That said, are you going to say this game developer has no idea what he's talking about regarding fast on chip memories such as what's used in the Xbox One as ESRAM?
eDRAM can look beneficial in previous generation, it was used in 360 and PS2, but you know why?
because devs at the time were stuck at slow DDR2/DDR3 RAMs. today eSRAM have almost no benefit compared to GDDR5. also eSRAM in X1 doesn't have large bandwidth at all, if it was using a huge bus and running @ 1000gb/s I would agree that it would hold an advantage to GDDR5 used in PS4, but sadly it's not.