I suggest that PM ask for help in SOPW for solutions to the backwards compatibility issues that they face.
Because if PM wants to keep its backwards compatibility issues a secret then there will be no work done to improve it.
I am currently rewriting my own web framework/CMS, so I don't have programming restraints that prevent the code from moving on with life. The only thing that was holding it back was the theme design but that's fixed with new and better capability's.
I would not do any work on this site till the owner agrees to use BBcode in it. Do you think they would agree to that?