The more I work on Hollo, the more its Mastodon-compatible API feels like a straitjacket. I chose it for a practical reason: people could use existing clients, and I wouldn't have to build a frontend too. I still think that was the right call at the time.
The problem is that clients can only expose what Mastodon's API represents. I keep coming up with ideas, then asking whether the API has anywhere to put them. If it doesn't, I have no way to get the feature in front of users.
ActivityPub API (so-called “C2S”) might be the eventual answer, but it doesn't help much today. I don't know of any clients Hollo users could realistically use with it, and adoption is still limited.
So I keep coming back to the idea that Hollo will need a frontend of its own. I'd keep the Mastodon API for existing apps. I'm not especially eager to take on a whole frontend, but I don't see another way to try ideas that don't fit Mastodon's model.