>Question: directly across University from where that branch of Shattuck ends, it looks like there was once a street (?) heading northeast towards Oxford Street. It's quite apparent on the aerial view on Google Maps, and the new apartment building on the site really shows the odd shape of the lot.

The property parcels might reflect a possibility of this "street", but as far as I know, it never existed because the Atcheson Physicians' Building and the one which was torn down just to the west of it for this new building are quite old, showing up in photos from the early 1900s. Shattuck Place has to do with the SP (or predecessor) constructing a station on the east side of their tracks near Addison St. when the line to Berkeley was built, and the Key Route building its line on the east side of the station building in 1903. Walnut St used to run all the way to University from its northern intersection with Shattuck Ave, but the block between Hearst and Berkeley Way was abandoned when the State built that building, which was moved from a location just east of University and Oxford on the Cal Campus, about where Mulford Hall is now, and expanded.

The clip at the corner of Oxford and Hearst is relatively new (c1970) and has since been abandoned in favor of a bike lane because the pedestrians never looked before crossing it. In the small triangle of land resides the sole surviving steel overhead pole for the Euclid Ave car line.

There is one such "street" on the west side of Broadway, about 2 blocks south of Oakland Tech, which is part of the r/w for the proposed line to San Jose. It's always been a parking lot.