Shimano's Secret Black Box
I've said it plenty of times: Shimano's new E-tube platform for the Di2 component groups is the best thing that ever happened to electronic shifting. Not only did it bring improvements like smaller connectors, no-fuss waterproofing, and lighter weight, but it represents Shimano's commitment to keep the same wires for the foreseeable future. This means once you go through the relative headache of doing all the wiring, you can basically just upgrade the extremities of your drivetrain, leaving its nervous system intact.
Regrettably, the newest wiring junctions leave a bit to be desired in terms of minimalism. The big 3-port and 5-port junctions (part numbers SM-EW90-A and SM-EW90-B) are big and bulky, and don't do a good job of hiding out of the way like the original "Junction A" on the first-generation Di2 7970. Moreover, in snazzy little stem compartments like the one built into the Trek Speed Concept, and our own TriRig Sigma, the new boxes are too bulky to fit. Shimano, it seems, wants you to run them external, taking away the ridiculously-awesome aesthetic of a totally-hidden Di2 installation.
The 5-port junction box is a bit tricky to hide, since it doesn't fit in the Sigma or other stems like the Trek Speed Concept.