The 757 and 767 cockpits and deck angles were designed from the beginning of development to have similar perspective and the least amount of differences to obtain the Common type.
The Crj 700 had too many differences noted right up to the time of certification to gain same type status. There were nearly 200 differences from what I remember. Somehow, (wink and nod), they were supposedly reduced to about 149 (not sure of the exact number) and gained certification to a lot of people's skeptcism and surprise, just under the wire of the minimum amount of differences as set for by the certification rules.
One airline I know, decided to keep it safe and keep it separate. Their FAA office was in agreement and also would not permit them to operate both aircraft. Shortly thereafter, a European crew, who was flying both, cracked up a plane on landing due to dissimilar landing perspectives in a morning landing that had some visability restrictions due to fog.
The 200 has so many ADs and Operation Bulletins out, it would be extremely difficult to fly both and keep things straight--especially with tired crews.
It's all about saving bucks. Put everybody on the lower pay scale for most pay events, and then give a paltry premium when a pilot gets to fly. For a company that is currently flying the aircraft separately, it would be a pay cut for the people on the 700, and an occasional pay increase for those who do not and usually cannot hold it. In other words, concessionary, but not shared by all. It amounts to Industrial Cannibalism.