Newly opened Chase Center (opened Sept 2019) also has a Muni Metro stop. The T Third Line was already there before it was built, although the platforms were split into a northbound side platform and southbound side platform. During arena construction, they redid the station and combined it into a single island extended platform, to accommodate two two-car trains in each direction.
To me it seems like a no brainer to add an infill station to an existing line to service United Center especially in a high public transit usage city like Chicago.
https://goo.gl/maps/Bw6HiRpfCLDqrdyH8
When the Central Subway extension opens, the T Third Line will merge with the Central Subway to connect to Chinatown going through downtown SF rather than looping around the Embarcadero.
