I remember there was research into this idea in Cherno Quest, and then vs now, I think realistically I don't think a high-speed transport system like that is viable. Beyond ensuring we have at least one Jaeger stationed in the new city at all times, I think we have two potential options:
1) Upgrading our scanners both in Seattle and the nearby cities to high enough level that we can guarantee we can catch any Kaiju well before they could get to either city - at a level well beyond a mere 6.
2) I know it may sound crazy, but think realistically we have a better chance of researching some kind warp/wormhole portals for instant city-to-city transport than we do making a physical high-speed transport system work. Flying through the air at those speeds risks damaging the Jaeger on landing, and ground system risks being wrecked by Kaiju and risks being impossible to keep repaired feasibly.
Alternatively, I think for the short term we're better off making contact with southern California - if they do have a working Shatterdome and Jaeger down there and are pulling off the same show we are, making contact with them and establishing relations and communications is likely to provide us with the best of what we need (mostly research) while removing the need to split our limited resources between multiple cities.
One point certainly, maybe two points, I'm not sure on three at the moment - we do have our limited resources to consider, especially with our plans to build additional Jaegers and power cores to run them. I expect the needed Supercells to cost a pretty penny for the foreseeable future, even with cost reduction research.
