Matthew Brooks Robinson Yeah, sorry the photo was misleading. I wanted to show internal structure.
For networks (electric, Ethernet, pipes, plumbing), it is easier to dig into straw bale than into cemented blocks or bricks

but I prefer to use counter partitions with room for those networks, also for the sweating of the pipes as you mentioned
Regarding costs : 10 times less for material, 3 times more for workforce.
Most of the extra time (workforce) is needed for details to optimize thermal performance, which, one should do also when choosing "passive houses" standards, whatever the materials. One benefit of straw bale is: the simple fact of using them makes the building ahead of current standards in term of comfort: thermal + humidity management + noise. Easier to achieve high performance, next generation buildings.
I must admit, however, that straw bale cannot be used in any climate since humidity is its enemy... it must be used locally where cultivated (another benefit for the planet)
Regarding the modeling, don't you think drawing the inner of the wall being solely insulation might lead to problem for junctions of slabs for example? It also means my IFCs won't be accurate nor representative.