This is all about offering choices that manufacturers either didn't think about or don't care about. For instance I have a Specialized SWAT mount that is a Fizik ICS adapter. You know those two groups don't want interchangabilty they want to lock you in to 'their' stuff. Neither Specialized nor Fizik would ever build such an item. But if you need/want one then you will pay the price for it instead of trying to kludge something together. Your other options are always tape and glue, they can be your friend if you want to attach thing A to thing B when things A & B come from different people. 3D printing, in my mind, is for those single items you can't get anywhere else. With the exception of one single item on my Shapeways page I can easily count how many of some items I have sold (note some are 0 items). I can also easily count how many items I have on my bike, that wouldn't be there is I couldn't 3D print them.