Multiple clients use custom emojis. That's actually quite popular.

Highlights is a useful event and we're going to be implementing it for new use cases.

But... Yeah. That's typical for stuff that's just a client feature and not something that needs to be in a base protocol.

That shit don't scale, hence the frantic race for NIP numbers because they don't want to go over 99.

Would make more sense to just have an editable Event Kind List, with a link to the project repo where it's defined, so that people can figure out what they're looking at, when an event shows up in their relay.