[M T]

OF, there is no particular reason why a subdomain would be preferable to a new domain.  If the powers that be for this domain don't want it for whatever reason, I don't see why a subdomain would resolve those problems.

A new domain is relatively cheap.  Getting a host for it shouldn't be that expensive.  The big initial "expense" would be someone's time to set up the s/w (but I expect the current board's configuration would be available for cribbing).  The big ongoing expense would be the monitoring of new users, establishing policies & enforcing them.  Possibly plus dealing with any legal claims that might come ("You are abridging my right to free speech.")
As always, another expense that wears one down is the issue of updating the s/w to keep up with the source and to stay away from intrusions.  Too often people leave the s/w alone until it is way out of date and it is hard to update.

[M T]

OF, there is no particular reason why a subdomain would be preferable to a new domain.  If the powers that be for this domain don't want it for whatever reason, I don't see why a subdomain would resolve those problems.

A new domain is relatively cheap.  Getting a host for it shouldn't be that expensive.  The big initial "expense" would be someone's time to set up the s/w (but I expect the current board's configuration would be available for cribbing).  The big ongoing expense would be the monitoring of new users, establishing policies & enforcing them.  Possibly plus dealing with any legal claims that might come ("You are abridging my right to free speech.")
As always, another expense that wears one down is the issue of updating the s/w to keep up with the source and to stay away from intrusions.  Too often people leave the s/w alone until it is way out of date and it is hard to update.