How about a midi controller – with audio interface (like the NI Maschine MkIII), and a built in USB hub, that would front end to the new USB High-Speed Overbridge Stand Alone? (You supply the $400 PC.) The controller would have some mixer like interface functions, so you could run two voices from your A4 by your Digitakt, and mix a signal to the Heat – or switch that all up, etc. Or change the mixes on the fly, maybe even from a sequencer like on the Roland MX-1. So this box would have a USB-3 connection to your Overbridge host PC and a bunch of USB-2 High-Speed ports to all your Elektron gear. The audio interfaces (both in and out) would allow you to connect other (non-Elektron) stuff. Beyond mixer functions the UI would be a general purpose interface to Overbridge functions, like LFOs, filters etc.
Not sure whether it would have a display onboard, like the NI Maschine MkIII or Ableton Push 2, or if it relies on the display in you PC.
Seems like Elektron could price this in the price range of the NI Maschine MkIII or Ableton Push 2. Not sure if it’s PC, or Mac based or both.