It’s not the same thing because Unicode is the only gatekeeper for emoji adoption. You can’t use an emoji that isn’t yet in the standard and deployed by the OS vendors. Whereas OED only adds words that have substantial real world usage.

Re: monochrome emoji rendering — an impossible proposition if you need to render any user-generated text. People simply can’t understand that their emoji might look different than when they picked it on their iPhone keyboard. The supposed rendering latitude on emojis is completely imaginary; in practice you need to get an emoji set that’s as close as possible to Apple’s without infringing on their design copyrights.

> You can’t use an emoji that isn’t yet in the standard and deployed by the OS vendors.

You can, as long as you control the font. Pick any codepoint in the Private Use Area and have your font define a picture for it. That's the whole idea behind icon fonts.

> People simply can’t understand that their emoji might look different than when they picked it on their iPhone keyboard.

Android users who pick an emoji on their Google keyboard and then have something different show up in the message they sent seem to be able to cope somehow.

But if you can't get away from imitating the Apple look because of wrong users, you could still try converting it to monochrome. Maybe users will forgive the deviation if it makes sense in context, e.g. for a terminal emulator.

The terminal emulator is one of the places where I actually expect coloured emoji support.

Granted, that it's supposed to emulate a teletypewriter but I think that ship sailed a long time ago.

The analogy is that Oxford Dictionary is adding words, BUT ... you can only use those words and your words will be automatically replaced by synonyms on different platforms.