Re: Fine to plan 4 1st class decades from now, but a fix in the next year or two would allow hourly service that's good enough. Walk before running
IOW, do a
Dawlish. Would need to be closed only during Really Big Storms (maybe a few days a year). Would cost a small fortune (rather than a big one for moving back to I-5). Would likely work for 50ish years before climate change and sea level rise begin encroaching on it again. Which would make it, of course, somebody else's problem, so possibly attractive.
Coastal Commission, parks, and people living nearby would scream bloody murder and flood the courts with lawsuits about the uglification and reduction in beach access (because they would have to go to safe, separated crossings rather than climb over the tracks everywhere), and reduction in sand supply for the beaches (which is in fact a problem when serious shoreline protection is done). It could probably be sold to the blufftop property owners if things are stabilized enough to protect their properties from the erosion and landslides that are otherwise common along the seashore.
If you want to plan for 100+ years rather than 50ish, it does have to move inland.