I'm not sure why someone would want to just create an "shell" of a plugin that is an advertisement for something else. I mean how would it do the plugin author any good -- I can't imagine that these plugins would gain any kind of traction. I mean wouldn't users just rate them down to zero stars?

I personally have a plugin (Pretty Link) in the repository that is very full featured -- but allows people to upgrade to a premium version if they want. I've found that by providing as much value as possible even in the free version of a plugin -- it gets people using your plugin more which allows you to "continue the conversation" -- which I think gets them more interested in upgrading later.

I really wish that more premium plugin developers would operate this way because I, for one, would be more likely to purchase them myself if I were able to see the value in them by using a free version first.