Tim Beiko suggested using the Ethereum Magicians forum as the hub for structured community proposals and feedback during the early stages of upgrade planning

Quotes that support claims

Headliner proposals (starting at PFI) should be structured explicitly via Ethereum Magicians threads that follow a clear template such as this:

Open Call for Proposals: At the start of each upgrade cycle, as the previous fork approaches final implementation, AllCoreDevs clearly announces an open call for headliner proposals. Champions submit structured proposals asynchronously on Ethereum Magicians, explicitly aligning their proposal with the established Fork Focus.