It's the Accela, which is the "fast" commuter train. The maglev train, if implemented, would be the replacement for it. So it's a pretty direct comparison. And you are correct, it's a commuter train but full to the brim with capacity of around 300 people. Runs from Boston to Washington and I would guess that the stop with the biggest boarding delays would be New York for obvious reasons. Of course you can't count the process of passenger loading in Boston or Washington because they are terminal ends and don't figure into the train schedule. At Philly it will generally take on about 50 people I would guess(but there are 12 doors so generally only like 5 passengers boarding per door), with maybe half that number getting off. Similar for Baltimore and maybe half that at Wilmington. The other stops have much fewer people coming and going.
The bigger problem by far is the fact that there are ancient bridges and tunnels that you have to slow waaay down to go through, by law, as well as local zoning restrictions for safety and/or noise reasons that also make it slow down. So even though it can go something like 100 MPH it's only permitted to actually go just a little faster than the older trains. So unless the japanese want to pay to rebuild all those old tunnels and bridges, and reroute around the towns, this project makes no sense.