The project was originally created to run programs from a MicroSD card on an ATmega16 (without reprogramming it). SBI is a generic library (platform indipendent) that lets you run programs from a stream (es. File). The programs are a sort of bytecode, and they are interpretated at the moment. So you don't have the better speed, but for now this is the only way to run programs from RAM (or SD) on Harvard architectures.