It appears that I finally got the acceleration working on my MSI Gaming X RX 480 4GB. Wasn't sure what helped exactly as I was messing around and trying every method I could find online....
My current setting: Mac mini 2012, Akitio TB2, MSI RX 480, Dell DA-2
Following are some of the things I did before my last restart, they may not be execute in this particular order since I already run some of them prior to this restart:
disable SIP
update AMDRadeonX4100.kext with RX 480's ID
update AMDRadeonX4000.kext with RX 480's ID (in the Baffin section where there's pretty much empty...there's a good chance that this won't help but I just list it here..)
update 9500 controller with iHEX so the name displays properly (see this guide here: https://www.theitsage.com/install-radeon-rx-480-gpu-macos-sierra/)
fix kext permission with kext utility
clear(or rebuild) kext cache (tons of error message came out...didn't bother to read all of them...)
run the PlistBuddy codes in this thread posted by Hedge under Kext Mods section:
run Goalque’s AMAZING automated-egpu script in -a mode
restart with eGPU plugged in and HDMI plugged in eGPU
And viola! RX 480 is working