As I understand it, BA would like to have OZ based crews so that the UK crews would do the LHR~SIN, layover and return. The OZ crews would work SYD~SIN, layover and return. This would greatly reduce layovers down route but this was not agreed, many years ago.
I sit to be corrected and I think that numerous carriers would like to do this, perhaps some do. It would be interesting to know.
Coincidentally, there is an identical problem - but sort of in reverse - in British railway ops. The old BR (so I suppose the new companies) wanted drivers to operate to the max of their hours then layover and work a return train the next day. But the (long standing) agreement is that they work half their hours, then turn and work back to base, so that they always get home. This can, I gather, cause waste of time as they may have to wait longer than statuary rest period at the turning point for the return service to operate back. Again, I sit to be corrected.