Thanks for the link. That's an informative web site. Here's the top-level link for all of their rail project construction: [octa.net]

Note that the kind of wall they're building isn't really a permanent retaining wall. It's more of a heavy fence intended to keep small amounts of material from hitting the tracks right away, holding it for removal in ways that don't close the tracks (or a road) for extended periods. Example: what they built at the Casa Romantica: [octa.net]

That's what emergency funds pay for: just getting it open again. A true long-term solution for that line, as at Del Mar, requires that a new railroad be build inland someplace, like along I-5. That would cost billion$ not million$. Intermediate, they could build actual retaining walls and make it kind of like Dawlish, but the Coastal Commission, the State Park (much of the San Clemente beach is a state park), and lots of private landowners would have an interest in that bit of "uglification" so I wouldn't expect much of that to be done.