The A2O core was a follow-on to A2I, written in Verilog, and supported a lower thread count than A2I, but higher performance per thread, using out-of-order execution (register renaming, reservation stations, completion buffer) and a store queue. It is now being updated for compliancy and integration into open projects.
Why do you think that https://github.com/OpenPOWERFoundation/a2i is a good alternative to a2o