Old thread but I just wanted to share. I gave up on the E750 replicator, it either is dead or only works with the exact USB C that it came with. Unfortunately I lost that so I just gave up on it. Fortunately I just picked up one of these on amazon. TP-Link UE300 V4 https://www.amazon.com/gp/product/B00YUU3KC6
This uses the RTL8153 from what I could find via google, however I installed the RTL8151 and RTL8152 drivers and the dongle was recognized as ETH1.
Once you have added this to the hotspot as ETH1, you just have to add that to the LAN interface via LUCI. Just go to “Network” then “Interfaces” and edit the LAN. Go to Physical Settings, and under the “Interface” pull-down, check the ETH1 interface to add it. You should then be able to hook up any ethernet device and get a dynamic address.