Language models are not like the Classic Theme, which can be relegated to an extension (now defunct).

Language models are like Hello, Pocket, and Sync. Core browser features one and all that must silently run by default unless explicitly disabled.

Sync is the only feature you listed which is arguably a core feature, in that it makes sense to build into the browser to be able to sync as much of the browser's settings and data as possible for the user. Everything else --- Hello, Pocket, and LLMs --- can and should sink or swim as extensions which the user must seek out and install if they provide sufficient value.

You won't find much relating to Pocket or Hello in the OSS project. I predict a lot of the new AI functionality will stay out too. So not core functionality.