I've been working on an accessory-cage based quadcopter design to have a modular way of adding and removing components. The intent is to avoid the rubber-band and tape method of attaching components to the airframe. The accessory cage is comprised of four vertically-oriented carbon tubes and is meant to hold everything but the motors. There's a 3D-printed stage for each component; the flight controller, battery, ESCs, etc. each sit in their own carriers that slip on and off and can be repositioned as one sees fit. I have a basic "starting point" CAD model for an accessory stage, and I modify it as needed for whatever component I want to add.

The design needs some refinement: I'm going to implement a better thermal break between the motors and the [low-melting temperature] PLA airframe. It also has underside LED lighting (not visible in the pictures) that I would like to make removable for wiring access in the next version. I designed and printed prop guards but haven't installed them because I don't want to mess with the aesthetic and add too much weight, so instead I have minimalist stainless spring-wire prop guards in mind for v2.

Once I'm really happy with it my hope is to upload the files to the Thingiverse for those with a 3D printer, if anyone is interested. I'll also include the "starting point" file for the accessory stages, as well as the Inventor part files (2009) for anyone with access to that program.

You'll note in the pics that the flight controller is simply supported in its stage, so I should also work out an isolation web for it (maybe something like a shock mount for those old-timey microphones).