Anybody can set up and host another PHP-BB forum; that's the easy bit. It's been done a few times; almost nobody will go there.
Accident discussion should not be suppressed because that is how one learns. The AAIB reports come out a year later when almost everybody had forgotten about it, and by the time the text has been agreed between the various parties concerned, the report is likely to be pretty bland.
For example I can recall one fatal accident in which IMHO a major factor was really negligent engine maintenance, but the report did not blame the maintenance company at all. This helps nobody. Such companies should be named and shamed - probably by PM to avoid getting sued.