Hi,
there are Ethernet to USB adapter for devices which do not have an RJ45 Port. Allthought the USB Port on the Mikrotik routers are mainly for mobile Interent Dongle or power, i wonder if it is possible to use an MikroTik Router as ethernet adapter. Like this configuration:
[Device without RJ45] ---- USB ---- [mikrotik] --- Ethernet --- [Switch/Modem/Router] --- Internet