I don't tend to visit here much any more, but thought I'd chime in.
Really PunBB is 2 things:
An open-source forum software.
The forum software itself is released under the GPL. Anyone who wants to can take a copy, start their own community, and maintain/develop it as they wish. This is exactly what we did with FluxBB. There is nothing stopping you (anyone) doing this with PunBB, and creating their own version - as long as they abide by the GPL.
The other aspect is the brand PunBB. In other words, the name PunBB, the domain, and the community. This obviously is a harder aspect. You can either create yourself a new brand, which takes time to build up and become known (as we did with FluxBB), or attempt to obtain PunBB from Informer. I think the chances of this are fairly limited - Informer paid a good chunk of money for PunBB and aren't going to want to just give it away.
The most likely option here would be to put together a team and try to make a deal with Informer, whereby you as a team/community are responsible for the development and maintenance of the software - but Informer maintain control of the brand and copyrights.