Hey Danny,
When you make it exclusive for those holding a current license or in current employment it sounds as if you might also exclude the retired members of the fraternity who have a lot of experience to offer, and who were active when they first joined PPRUNE but have recently retired. I hope this is not your intention.
However, PPrune is a *professional* pilots' forum and I do think we should only have professionals contribute and yes there has been more than enough 'uninformed opinions' from wannabes and passengers which should be excluded or confined to a sub-forum. Besides, there are countless Private Pilot Forums on the Web anyway.
You may have to do something similar to what the airline forums do on this site and have a staff verification, but whatever system you decide on it is going to involve a lot of work screening, even if people send a JPG of their License for you to check you may have to recruit helpers.
I think the easiest way to do it is on a TRUST BASIS. Until current members attach a small sized JPG of their license page they are considered UNVERIFIED PROFESSIONAL. If on eventual inspection (at your own pace) it is found that they have uploaded a jpg of a library ticket or Mickey Mouse then they can be publically shamed and deleted.
All new applicants however need to upload a jpg of their licence immediately to gain entry. I am not sure what bandwidth load this may place on your server but I think it may work out fine. Once you have verified them you can delete the JPG.
But please do not exclude the retired fraternity and please allow old licences to be accepted.