IMHO the assumption that parsing the SQL is the bottleneck here is unfounded - I'd like to see some analysis supporting that first. The queries used in those benchmarks are extremely trivial, and there are far more expensive operations involved. I don't think it can be deduced from comparison of two quite different benchmarks (different workloads, different dataset sizes, different hardware, ...)

Also, relational databases are general-purpose query engines, not caching solutions like memcached, with very limited set of commands. It might be possible to invent a more efficient binary protocol to send queries/receive results, but then you still have things like optimization, planning, permission checks, ... that are usually more expensive than parsing the data.