Well this is a stupid idea if ever i heard one. Talk about creating trouble for your own staff. Having just paxed on a q400 yesterday from EXT (nice flight thanks all) there really is stuff all room for hand luggage compared to say a 737. So with a mixed fleet the customers will be completely confused as to why their 146 compatible hand luggage now has to be checked in "£4 please" when the dash is on the route.
Hmm i see lots of rows at check in come Feb.