I took apart my controller and did the thing, I now see a black screen with the text "4.3(USA)" in the bottom right corner.
yep, we got 'em..If you got into recovery mode and it shows "4.3U" in the bottom right- most likely BT module issue.
Well, since you even tried to restore your NAND, I think BT module is indeed the problem here..
You could either try to get them online or find some junk Wiis around and swap from there.