And why would Brussels clarify anything before the actual process starts? If they did, other countries could start asking "you know, purely theoretically, if we wanted to leave, what sort of deal would we get?" and that would be just stupid. It's like saying to your wife "you know, if I decided to divorce you, how would we split everything?" - if you want a divorce, then say you want a divorce, doing anything else is just making the whole situation sour.