In an action that went largely unnoticed last month, the CHSRA has changed the specifications for platform lengths. Whereas they were originally to be 430 meters (long enough for double trainset), they will now be just 800 feet (243 meters). This will effectively cut the capacity of the system in half.
The memo does allow for longer platforms at shared stations — if other operators are running longer trains. Its effect on the cramped Transbay Terminal is unclear, as Caltrain is only planning for 8-car EMUs.
The decision also affects placement of turnouts and crossovers. So once the track and platforms are locked in concrete, it would be extremely difficult and costly to change later on. Reducing costs of the project is one thing — but this is an example of being penny-wise and pound-foolish.
Double trainset
Systemic Failure 
Seems to me like this might not make much of a difference at minor stations. People heading to or from those stations just get assigned seats on one of the cars that opens its doors at that station, and they’re unlikely to run into capacity limits, while the other half of the double trainset acts as an express. So it’s mainly SF and LA, and maybe one or two other stations, where you want to be sure to have the longer platforms.
Of course, that’s probably the issue…
I see your point. They could run long trains that only stop at SF->SJ->LA-AH and skip the rest.
Alternatively, if all trains are “short”, then HSR can park 4 trains in the two platform tracks in SF leaving more tracks for Caltrain.
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VTA’s Winchester extension was built with two-car platforms, but track was aligned such that more cement can be poured for three-car trains. Unfortunately, it seems like they are doing more drastic cuts here and not even allowing for that.
Blech. At the very least, SF and LA need long platforms.