Basically, if you have any problem with these Mac’s related to hardware on the main board. You will have to replace the main board.
I think this could become not cost effective out of warranty. I mean in the past if you had a storage stick or RAM go bad you could just replace that one part. Now since they are soldered you most likely will have to replace the entire circuit board. I don’t know how much Apple will change for these boards, or if pulled parts from other units will be available. But clearly this will probably add to the cost of an out of warranty repair. Apple is not the only company to start doing this, but it is a popular trend in many computers. So we get the right to repair, but the costs of doing so may become impractical.