I've been working on a custom circuit board I am calling the "mavboard" which will be a board that will distribute telemetry connections to various other devices, and allow you to select which port gets the telemetry Rx pin, since only one thing can talk *TO* the APM telemetry port. All other mav ports can sniff the APM Tx pin.
As you can see in the images below, I went a step further and embedded an ATMega directly into the board as well. My vision for this board is not just a "Mavlink Hub" but also a protocol translator for a couple of popular RC Rx devices that offer telemetry options such as FrSky and OpenLRS. What I have working so far is the FrSky conversion originally based from JDrone's jD_IOBoard_FrSkyMAVLink project with refactoring and bug fixes from Vito Ammirata. We have been discussing and making progress over in This Thread and his updated code has been put into GitHub.
When done, all the board design files and schematic will be available for download. The initial prototype is using a number of through-hole components which I would like to switch out to SMD so the board can be smaller (shooting for size of MinimOSD), but I am still exploring options for how to get a small number of SMD boards stuffed without having to hand solder all the components. If interested, I may offer some up for sale so I can get a batch of them made.