Interesting, but perhaps a bit over-the-top (or under, since it would have to all be in tunnels).

Current planning is incremental based on correcting the stub-end nature of Union Station. This scheme would effectively abandon Union Station other than as a transit connection, and is anything but incremental. It also makes no sense unless fed by a total Electrolink rebuild, including lots of grade separations and multiple track, supporting 24/7 high frequency operation like a NY subway line but at full railroad (80-90 mph or more) speeds, is done. BART for the 2050s in LA. I question whether LA has the travel demand for transit to support that level of service on the long lines, but am open to credible data and analysis. First thought re. cost for the total job would be on the order of what we're planning to spend on the HSR starter line from SF to LA, and the increments of development would have to be large. Then, most of the lines parallel existing transit in downtown LA that's hardly overused. Maybe the cost could be lowered a tad if Elon's Boring Company could figure out how to magically build BIG tunnels (rather than little ones) faster and cheaper than we can now.

Considering our current, usually budget-enforced, incrementalism of transportation planning, I really don't see this going anywhere other than an interesting thought experiment in a blog. Still, stranger things have happened, so happy dreaming and in the meantime lets get on with the run-through tracks that can actually be built in the foreseeable future, are needed now, and will work with existing trains.