>> I think that the confusion is that the original poster is suggesting that providing combined builds would help to ensure that changes in the source tree that were MAME or MESS specific would compile for both MAME and MESS build flavors. Thus the goal to achieve is greater robustness of the MAME/MESS code by testing combined builds more frequently. <<
It still sounds like self-serving purpose. "Robustness" is too vague term, not sure what practical benefit is supposed to be and why is "increased robustness" desired in the first place. The more parts something has it becomes easier for it to fall apart, so I don't think MAME & MESS can possibly be more robust combined than separated.