Although the S&S couplers are wonderful, and we do put them on many builds, they also come with a pretty wonderful price.
We had a project a few years ago where the goal was to build a separable touring bike that would fit in a 25 by 25 inch case and when it was done we were able to pack the bike in a 20 by 20 case... this includes the racks as the rear one breaks down and packs flat. We used telescoping tubes and pinch bolts up front and the rear connection integrates with the seat post... the bike breaks into 4 pieces.
This bike fits in the custom made case with it.
This technique was used by some very famous frame builders like Rene Herse long before S&S couplers appeared on the scene and you do have to be an approved frame builder to use them.
Using S&S couplers would have increased the price of this bike dramatically.