I do really like the CRJ-550 as it fixes a lot of the issues with the CRJ-200. Newer, first class and economy plus seats, and WiFi. It burns about 8% more fuel than a CRJ-200, but fuel is cheap, and just a few % revenue premium for having first class and economy plus seats more than make up for it. I’m surprised United hasn’t replaced all the CRJ-200’s with CRJ-550’s.
I do see the CRJ-200 going away in the next few years, but I definitely do not see 50 seat RJ’s going away.