Extending options for different plugin types?
IMHO, there is no need for this and I don't think that there is a problem that needs to be solved by Craft based on what you've outlined. Additionally, putting this on the roadmap may lead to a confusing API or at the very least, it might get us into a convoluted plugin philosophy like in EE, where we have plugins, modules, addons, etc.

Currently, plugins can decide whether they have settings or not and the API that enables that seems very eloquent to me.

Having said that, properly categorizing plugins will be very important and I would bet that the plugin store will address that; )

Please let me know if I misunderstood what you were trying to communicate.