I also think there is a over simplification of what peoples needs are and where they put those needs. For some it is just a box for extra water, for others it is a place to put their filtration, reactor and dosing needs, etc. Your systems needs will change with maturity. Someone needs to be motivated to build a sump that can be configured to add or subtract modules. It has been semi-attempted before, but never successfully. One may start out with a refugium for nutrient export on a new tank then want to change it up later when they have to shut the fuge down because the coral is sucking up nutrients faster than you can put them in. Maybe then use that space to create a frag area or a cryptic fuge to pull out DOC's etc. Our sump configuration is based on problems we have to solve, some people have different issues based on the size of their water volume, lighting, type of rock used, so many variables the list can go on forever.
Success in reefing comes from understanding what works within a certain set of variables. If you add a new set of variations you must come to a new understanding to continue that success.
Ergo: "What works for one may not work for everybody"