Some interesting thoughts there for sure.
Re Auto_HTML - don't forget you can use the nodegen project to convert a subflow to a node - not perfect by any means but does help create the html config pages for you. Also @Steveorevo has just released this project that may help - Node Maker is here!
Re type checking - when we have considered this before - we always came up with more exceptions than there were rules. The number of times they would "get in the way" and slow down developing (say) a function node by having to create a ui to create this schema that can cope with many levels deep (as many nodes output objects not simple types - which then need to be expanded etc etc)... just makes the complexity (both in implementation/maintainance and user understanding especially for beginners) seem to outweight the utility. Instead we try to encourage creators to provide consistent info for the sidebar that describes what nodes accept, both mandatory and optional, and what they output. Also one of the key aspects of the flow is the ability to pass through other properties - so they would all have to be ignored, and many properties are optional etc.. All in theory do-able of course, but....
