However, this just isn't true. It would be possible to design a chip that only performed scrypt and pair it with exactly the right amount of ram, and it would crush generic hardware in terms of efficiency. Specialized hardware is always going to be faster than general purpose CPUs and GPUs, especially for highly parallelizable tasks such as mining.
Except that there's no "exactly right amount of ram" for sCrypt.
sCrypt, like bCrypt is defined over a largeish table which is constantly accessed and modified, both in size and content, during the algorithm's run. The amount of space this table will take up is effectively a pseudorandom value dependent on the message so each hash will take a different amount of RAM than the last.
That's the entire reason sCrypt based altcoins were supposed to be GPU resistant and should still remain ASIC resistant: their memory requirement is both large and random and the algorithm itself is designed to access that memory as much as possible, thus making performance of a brute force attack against it heavily reliant on memory latency.
Again, I haven't looked at code to say how the GPU miner actually works, but the theory was that since all but a very very tiny amount of GPU memory is "pooled" in such a way that only one core can access it at a time, any GPU miner would have most of its threads deadlocked for use of that one shared resource most of the time. I'm tempted to say that the miner probably uses a very clever workaround to solve the locking problem, but I sincerely doubt that they've found a way to sincerely perform brute force against sCrypt without maintaining and heavily utilizing that large table in shared RAM.
I'm not arguing that an ASIC couldn't be built, just that it's unlikely any ASIC will have significant performance gains over mass-produced and readily-available CPUs. CPUs are already very close to ideal for this application and any optimizations gained by building a custom one-use-only chip are unlikely to be economically meaningful, regardless of whether such an increase is technically meaningful. If you produce a miner that is twice as fast as a CPU but costs 4 times as much, I don't see people lining up to buy it.