For the initial iteration of minion cores, think of them as being an openly documented boot core and a way of implementing low-speed I/O in software (with some extra hardware support for things that would be dumb to do in software, e.g. shifting out a register). The initial target is SPI, I2C, I2S etc. Over the longer term, we are interested in using modified RISC-V cores for high-speed I/O and in general increasing the flexibility of a typical SoC design.