since this is a topic of discussion, what do you guys think would be a workable post limit for probationary accounts?

Still default 3 post max per day is good limit.
To curb rampant spams.

Perhaps add in limit 1 thread opening per day. It justified enough if legitimate probationary account to post serious discussion like instances in Serious Kopitiam.

ok. just a quick note on our current direction for new members.

we have rolled out invite codes for around 100k current members. If you've got an account registered before 2020, and you have logged in at least once in the last 2 months and your account is not banned/suspended, you would have an invite code in your Control Panel. This code is currently limited to 2 per member.

The invite code is currently needed to sign up for a new account, but this is while we iron out any bugs. Once everything is up and running, registrations will no longer require the invite code. The invite code will however be needed to get out of probation. Probation accounts will remain probation accounts with multiple limitations until a current member shares their invite code.