@bea
I think what we need for fun side is namespace (each instance has their own emoji).
I currently feels make rule to put emoji definition on public/emoji.json(or provide definition on API) and refer them with :shortcode@domain: perhaps works...
(Note: I wonder that fun things are acceptable (fa-spin was killed))

@bea
Alternative: send emoji as img tag and download emoji images to instance when toot arrived as we does for media to protect privacy.
l feel it's proper way to federated with GNU Social and so on...