With reference to https://premium.wpmudev.org/forums/topic/enable-specific-plugins-themes-depending-on-service#post-199802 from masonjames that :
"We're working to implement integration with our Pro Sites plugin. Then you can use this plugin to create your packages or 'levels' and assign them to accounts within WHMCS ... his feature is on the list - we're talking weeks away not days." - that was 3 months ago.
So, how's the integration of WHMCS plugin with ProSites?
Basically, I'd prefer to use WHMCS as the main payment and user admin. But would like to control the premium themes and plugins paid site members can use (and activate themselves) - which can only be controlled by ProSites for now.
Another question here is - instead of integrating WHMCS plugin with ProSites, why not create another plugin for superadmin just to control the plugins that members can use (which they will activate the plugins they want themselves)? Won't this be cleaner than integrating with ProSites which also collecting payments?