Daily News, Los Angeles, CA, 1/27/22:
LA Metro board OKs new light-rail line from Artesia to Union Station
The LA Metro Board approved a 19.3-mile light-rail line on Thursday, Jan. 27, that would take riders from Artesia to downtown Los Angeles, a first-of-its-kind transit project serving lower income communities in southeast LA County.
I don't know if the A Line can handle transferring passengers during the phase where the branch terminates short of downtown. It does make sense to continue this line to Union Station, especially if the existing infrastructure of the A and E lines downtown, as well as the Downtown Connector, are at capacity and could not handle another route interlined with them. On the other side of the coin, in a sense some may consider a branch to Union Station as redundant, seeing as how the Downtown Connector is going to bring A Line service through downtown to, you guessed it, Union Station before it continues over what is now the L (former Gold) Line to Pasadena and eventually Montclair.
Can't say for sure, but I believe I saw on a map in the past that the Santa Ana branch line would get the letter S.