Yes, this, a thousand times this!
(Didn't know about the Kay thing - I'll go find out more, I'm uneasy by the long shadow Papert casts over CS education)
So, asking the right questions, back to the 'minimum "useful" OS' - useful to what?
If you threw this question couched thus to the Fedi, can you blame the respndents for interpreting 'useful' based on their reality tunnel, and come back with a text editor, a C compiler etc...?