What is the main technical problem?
I now that scrypt algorithm needs more memory to run. But in GPU, like 7970 processors has not so many memory for random access (usually cache N KB). FPGA on the other hand contain N MB of BRAM, faster than cache.
Slower part (random access too) is 2-4 GB DDR on GPU, but FPGA board may have multi-port DDR interface and also be faster than GPU.
What about ASIC - there is no problem to get SRAM on it up to 500 MB...
Can anyone answer?
It is being worked on.
https://forum.litecoin.net/index.php/topic,2702.0.html?PHPSESSID=s04ugtai6e6v1fq7m96381m533