I do not make any special effort to sound negative here, but honestly that SoC did not really work on anything. Most of the stuff posted to Opencores is in fact half-finished, buggy projects, and Milkymist SoC does not use any other Opencores stuff than Wishbone (and still, this was because of LM32) for this very reason.
Even the OpenRISC GCC/glibc toolchain was crippled with various major problems until recently. The OpenRISC RTL still is, but I can see things moving in the right direction. Maybe Milkymist SoC will integrate OpenRISC at some point, if those technical improvements happen.
OpenSPARC and LEON were also considered, but they are very heavy resource-wise.