Why do you complain here and not at softaculous? They are a commercial company that sell apps packages and has built its software around cpanel and if you want that they support ispconfig, you will have to ask them.
ISPConfig will release a app installer with version 3.0.5.
Regarding whmcs, there is a billing module for ispconfig available which is integrated into ispconfig. Sii ispconfig.org. Some time ago someone also published a module for whmcs for ispconfig.