Reddit already requires it in the UK

Yes, and do we have any numbers about UK usage before/after the changes? Do we have any idea of how many people there:

• looked for an alternative?
• looked for an alternative and were not satisfied?
• looked for an alternative and migrated successfully?

And for those that were not satisfied, what was failing to them? Was the Fediverse so bad that they rather go back to Reddit, or did they just quit social media altogether?

The UK started asking for age verification ~5 months ago. That should give us more than enough data to take a look at this objectively.