This might be also a solution. But I am not 100% sure this would work with the modbus binding as it only supports `Modbus serial slave’ and not ‘master’ on the serial interface. With TCP Master is possible.
Furthermore your Raspberry Pi would need to be close to the DuW (USB max cable length ca10m). With LAN your flexibel, you can even go wireless. And most of all it would not solve the problem with this ugly MICA plug.
There would be an approach with solves all HW problems. The DuW device has an USB Interface with a proprietary “Service Protocol”. You would though need to write your own add-on binding to connect with openhab.