about "plug-in" concept

Hi all, I'm developping a REBOL/View app (called the main app), and I want to make available a plug-in concept in this app. The features required for this plug-in concept could be : 1-a plug-in would be an other REBOL/View app whitch could be launched by the main app; 2-a plug-in could be installed or uninstalled in the main app, by this main app; 3-a plug-in could have a licence number or not : without licence number requirement , the main app could launch the plug-in any time. With licence number requirement, the plug-in could be launched by the main app only if this licence number is valid. What are your reactions for this ? Do you have ideas about programming this ? --- Etienne