There was some discussion about this a little over a year and a half ago when NW put in that big order for 44-seaters. Rumor has it they were going to make a dedicated type for the 44-seater with a plug removed, slats, and a higherpower varient of the CF-34. They wanted it to be able to get off hot, high, short runways at max gross and have a 4 hour cruising range with reserves without it being weight restricted. Instead NW opted to get a standard 50 seater and yank some seats out. Economics prevail.
I think they are looking for a customer who is willing to spend the extra money for the upgrades before they try to develop the type. 50 seat economics is not very good with the stock model to start with let alone with all the hot rod parts on it. The -200 is a very capable aircraft as it is. There isn't much need to upgrade it other than pilot cool factor.