There is a strong emotional effect at play, so it's hard to say what will happen. I know someone currently buying a house, and the question of what will happen when Article 50 is invoked has been a persistent theme. E.g. in London, thousands of banking jobs may hang in the balance, with at least one bank having made it very clear internally that once Article 50 is invoked they will start planning which jobs to move - something that for that bank alone will start to shift massive amounts in salaries out of London (hundreds of millions at least)

On one hand finally getting clarity might be good news in that some people who have held back might spend more once the uncertainty of the immediate reaction is out of the way. On the other hand for a lot of people it makes things definite and will cause more cautious spending patterns, and there's still plenty of other uncertainty.

It also starts the clock, which will make people speculate about the timing.

I haven't the faintest clue how that will make traders respond. What I do know is that because I don't have the faintest clue how it will make people respond, I'm acting accordingly cautiously, and have cut my spending considerably since the referendum, and I know many others in the same situation, and indeed the UK has a whole has seen consumer debt levels drop substantially.

All this to say that it is foolish to assume that it boils down to whether or not the actual event itself is expected or not.