Electrification appears to be required for some good reasons.
The inability of Caltrain to run longer trains such as we see on the NEC has much to do with the need.
Short ( 6 car ) trains are the limit in the foreseeable future due to too many stations having grade crossings at both ends of the platforms.
Train density therefore needs closer spacing than can be done with diesels during rush hours.
In reference to above acceleration curves with EMUs will help train density and allows for another car instead of a locomotive.
Multi level EMUs will help somewhat. Car specifications have not been issued yet stating total EMU height but some products in Europe are some what taller than Superliners.