Should the usb tag and the usb-device tag be merged? Over half of the 79 usb-device tagged questions are also tagged usb, and a good majority of usb tagged questions are simply about usb devices, not just the protocol.
sd and microsd should be merged as well. microsd should become a synonym, as a Microsd card is simply a different form factor of SD cards, with no electrical or protocol changes. Nothing special or unique about it.
one-wire should be a synonym of 1-wire. 1-Wire is the proper protocol name (I have already corrected the few tagged questions, but can't suggest a synonym because I don't have 5 votes in that tag yet).
Addressed in Tag cleanup, episodes XIII-XVII
line-power and mains. The excerpts are identical. Is there a practical difference? Should be merged and synonymized. As should powerline, though Line-Power or Mains should be the surviving one. Not to be confused with the powerline-communications