OK. I have a modest proposal:
Anyone can use any emoji they want.
To achieve this users declare emoji's in a known format the browser recognizes inline in text, which includes a content hash of the emoji they wish to use.
eg. ":T15PXExNem0xX:"
Browsers use a DHT and local emoji datastore looking to the DHT to fetch any emoji's seen in text but not present locally.
You may submit a picture to your browser to create an emoji, but it must be a 128x128 webp image. The browser calculates the hash, and puts it in your local datastore. You may now use this emoji anywhere.
A few things to think through here:
1. Would be nice to have an non profit come forward and make a nice big server act as a reliable hub to the emoji database. The nice thing is, basically anyone can step forward at any time and provide servers to the network. Anyone can serve the emoji to anyone as they are addressed by their hash.
2. Regarding offensive or hateful emoji's, I think the question "What if this is used to promote hate?" Is a good question to be asking. But try to keep in mind that the system I am outlining is meant to be communication infrastructure, not a platform. Think of it like a different way to write text. This system in and of itself isn't a platform at all, as the only way to discover and use emoji's is to see someone use it somewhere else. You can browse your local datastore, but that's it.
3. What about REALLY hateful or outright illegal content? IPFS is a guiding light here (in more ways than one if people are familiar with the project). Lists can be made of Violating content by third party organizations and browsers could be configured to subscribe to those lists, very similar to the way ad blocking networks work. Apparatus could be constructed from there to support DMCA and abuse reports and distribute block lists. These subscription lists are user configurable, in case those apparatus are captured or abused and users feel the need to revolt.
Likely more issues than this? I don't think there's anything that is insurmountable. But that's the rough outline. Instead of relying on the unicode consortium, take advantage of content hashing distribution networks to create user defined emoji's instead.
I think about a system a lot when stuff like this comes up. Because I ask, what would be the most popular examples in such a database look like? Do we think it would be close to what the unicode consortium laid out?