Moving posts from anywhere behind the pub paywall is surely a nonstarter, especially in bulk.
I'd take your extreme suggestion another direction: shut down new thread creation in the pub - only allow staff to create new posts for say, 2 months. Encourage all other chatter to be done in other parts of the forum during that time. Could go as far as lock popular non-sensitive threads with links to their new public-facing threads in chitchat (ie airline issues, the 19 year old thread that everyone just posts the current weather to, etc). I'd apply this to the EV subforum too - though not sure I'd make a new public section for it until there's regular discussion on topics to warrant it. Keep the safe space for the Tesla bros (the real original purpose for it, including at one point a request that only verified Tesla owners should be able to post there
) and new threads for upcoming EVs, charging / chargers, etc shunted elsewhere.
No need to 'lose' the old threads, either. Link to them from their new home for those w/ the paid membership, by all means celebrate what came before... but look forward to the new audience and engagement that can come from there.
The point would be to create new habits. Loosen posting restrictions after a month or two, and see what it does for traffic, ad revenue, etc.
