I think that wouldnt work. Then the people on these forums (quite possably myself included) would just make a huge amount of threads asking the mods about stuff. Such as why is the Cyclops still in or how come we cant plot our own bases? Threads tend to die when they get moved beond page 1 and not many of the new influx of people will use the search button (regretably) so they will just create more and more new question threads not knowing any better.
The PM's are a good idea but they need a set amount you can send to an individual person per day. Lets say you can send 10 messages to the mods a day, now this doesnt mean additional posts on the same message just 10 seperate messages. Personally I keep it down to one message if I have a question or two. But this will allow the mods some control over the influx of questions and make them tear out their hair less. As for regular members PM'ing other members I see no reason why it should be limited. As long as your not spamming the PM's and taking up bandwith with all the crap messages you put out then it shouldnt be a problem.
For the users who like to spam the fake "beta testing" stuff or things similar, they should have a penalty for doing such a thing. First off its not true information, and second I had atleast 20 if not 40 of those messages in my inbox at one time. Thats alot of needless messaging taking up space. If you are temped to send out a PM like that then you need to contact the Mods and get confermation on what your saying. Then and only then should you send it out, and only one message to one person at a time. I hate getting the same message from the same person 5 or 6 times in the space of 2 minutes.
As long as limits such as these (not saying you have to use them but its a thought) are enforced by the actual forum members and the mods in a joint effort I see no reason for the PM system to be completely scrapped.
Also you could designate in a Sticky or Announcement that all the questions should be PM'ed to one or two different Mod accounts where they will be answered as quickly as possable. That way your inboxes wont be flooded and when you have the time you can look in and see what you can answer.
Approval of situation A recognized. Commensing the Cromwell Invocation. Ability restrictions lifted for limited use until the enemy has been rendered silent.