Why bother?
In case of dual GEN fail, start APU. All network supplied, except galley.
In case of dual AC BUS fault, forget about the network. Only essential buses supplied by the RAT EMER GEN. What do you want the APU for. To supply the DC BAT and the HOT buses?
Losing HOT BUS 1 and 2 is not that bad, is it?
with the RAT we have all we need