As to demand for more 146 freighters it depends:-
On the economy picking up
COST and most important capital cost. Most short/medium freighters in Europe work a small number of hours per day. For this to pay the capital cost of the aircraft is relatively more important than the per hour cost.
One big advantage of the 146 is that it is very quiet, for night ops this is more and more important.
I think this is the situation in Europe, anyone like to comment on other parts of the world.