> Now you can build on top of such stack, I am sure you could come up with 100s of micro apps ideas

Will each app just put their data in a subdirectory of a user? If so, that reminds me a lot of GunDB! @Martti Malmi 

 depends on what they are doing and what paths are users giving them access to, but there is no enforcement of sandboxing like in say IOS or something.  

 Is there a concept of giving access only to specific files / directories then? 

 yes, authorising a 3rd party app involves approving a request for given abilities on given resources. Normal stuff.