@Mastodon I can see the use in having a default instance for smoothing the sign-up process, but what about making that instance a special one that is explicitly for noobs only? If you opt not to specify an instance when you create your account, you are deposited in the (still federated) noob sandbox instance, where maybe the admins post regular info about etiquette and platform usage tips, maybe some spotlight posts about specific other instances etc.

Then, after say 90 days, with plenty of advance warning, you are forced to leave the sandbox and choose a permanent home through an improved instance selector. This choice could even be auto-suggested based on which other instance's users you interacted with the most.

Doing it this way would help to acculturate new users, make it clear to others when a poster is a beginner on the platform, and support decentralization by letting people get a real idea of what various other instances are like before picking one to join, while still making it mandatory to choose an instance.