@antekh - why is that? Simply because a company won't be manufacturing any ASIC chips for this or because of some other restriction?
scrypt and sha-256 are different algorithms and in short words: scrypt needs more resources (more and fast RAM) than currently available FPGAs or ASICs don't have.
What is interesting is, that when I shopped around, I found quite a lot of FPGA PCI board that although dang expensive, had ridiculous computing power and pretty heavy amounts of RAM. Some of them used for development or medical imaging.