Considering that New York Avenue was going to have a freeway companion, I really find it hard to believe that US 50 inside the Beltway was not going to get an Interstate designation of any kind. However, I agree that all the different freeway segments would've lined up to allow a continuous I-66 to Annapolis, although I-595 was sort of a consolation prize for this missed opportunity.
As for I-83 not proceeding straight past I-695, there were plans to follow MD 25 for a couple more miles, and then arc it to the northeast to join the current alignment south of Cockeysville, but local opposition ended those plans, bringing forth the shared I-695 segment and an altered version of the Harrisburg Expressway onto the drawing board. Similarly, another alignment would follow the Light Rail tracks through a heavily wooded area to the city limits (a la I-70 through Leakin and Gwynns Falls Parks), but nothing came of that either. In any scenario, I-83 would change names at I-695: Jones Falls south of there, and Harrisburg north of it.