Modular. Open the lemmy interaction module as you said, allow people to easily create shims for the likes of kbin or anything similar like that.
Ill support whatever LJ decides to do, he's proved he's more than capable with what he produced in sync.
Open source is cool as fuck though
It gets them users, which are needed for funding.
Like it or lump it, AI chat integration is a feature, and lots of users (those who aren't on a federated group discussion Firefox) will see it as an attractive feature. "It doesn't even have a chat bot" is something that will legitimately be said if its the only major browser without it.