That was certainly what I had in mind, in full armchair CEO mode! I would envisage the C-Series as a replacement for the EMB fleet, with the Q400s staying.
A mixed Q400/C-Series fleet would be very flexible and fuel efficient. Dispatch on the C-Series is reported to be excellent and the Q400 has come a long way. The Q400 has good range and speed for a prop and does a surprising amount of the leisure flying, so I don't think its fair to say BE would drop the leisure flying if they could. Many ensure routes have high fares and good ancillary revenue.