For the people who currently ride the line, service would be substantially worse (less frequent, more crowded, and prone to merging delays with the express). And I doubt the express would attract many new riders.

The area from Cypress Hills to Bway Junction was only built for two tracks. Bway Junction to Marcy already has three tracks. Supposedly, if you run some J trains express, and they skip some of the stops along the two track portion, you can make it from Jamaica to Fulton st in 9 stops and 35 minutes, a bit faster than the LIRR to downtown Brooklyn + transfer to the subway. The eastern Queens to downtown commuters would be the obvious beneficiaries of this new route, but there would be benefits to anyone traveling to Chinatown, the LES, Williamsburg, etc from Queens.

I’m not sure what you’re getting at with the L. The busiest part of the line is west of the transfer points to the J/Z and the M. And the transfer point to the J/Z also happens to be the transfer point to the A/C, which is a faster route to Lower Manhattan than the J/Z (and possibly even a faster route to Midtown than the L – I’m not sure). Somebody commuting to Manhattan from, say, Montrose Avenue is going to take the L into Manhattan and transfer there, if necessary, to the appropriate north-south line.

Mind you, I’m not making that argument – personally, I doubt it would have much of an impact on the E. And it would be quite expensive, as the island platforms along Fulton Street would all need to be relocated. Also, there are two all-stop (J/Z) stations along that stretch – Woodhaven Boulevard and Cypress Hills. They’d need to be configured as express stations in order to provide them with adequate service and not to overload the local. Come to think of it, even with those two stations as express stations, the locals would still probably be more crowded than the expresses.

But I could be wrong.

Well I think the real problem is American culture. This is the same problem we have with health care that most developed countries don’t have. In our culture we live by the golden rule “If it aint broke, don’t fix it”. Essentially we have no concept of real maintenance, now yes for the NYC subway system we have a major problem, as it runs 24×7 it is hard to ever find times to do regular maintenance. It’s cheaper to keep things in working order than repairing things that are broken. If we switched to the idea of preventative maintenance we would be able to have more funds available to actually expand the system. Currently the development in the system that does exist is too Manhattan centric and projects like the Second Ave projects shouldn’t be considered a mega project. A mega project would be filling in all of the wholes in the system where there is no reliable transportation other than buses.

The NYC area has three huge projects — the Second Avenue Subway, the East Side Access, the Jersey Transit thing, Journey to the Earth’s Core or what’s it called. (Not to mention the #7 extension and assorted other smaller projects.) And so each of these three megaprojects has a federal share that works out at far less than half the cost of building them. If the feds were paying 50%, or better 60%, or best the 80% of 90% they do for highway stuff, then the MTA, the City of New York, the State of New York, and the Port Authority of NY and NJ would have much more money to put behind other projects, even repair and maintenance.

That said, I definitely do hope that in a few centuries once they finish it, that they move all the money they would have gone to new contstruction to rebuilding the present system and restoring it entirely to a state of good repair. It seems like if they don’t, the general deterioration of everything will if anything accelerate as the system heads into its second century.