I'm new here. This is my first post. I really like the LGA train extension and de-interlining of Broadway that's on vanshnookenraggen. There could just be one local service from LGA, through Astoria, Broadway, and 4th Avenue that never merges with another. Express service would still need to merge at 57th Street, but I think that point is better suited to have a merge than 42nd Street. The other question to ask is whether it creates more problems than it solves (as in additional merges). The and / merge at 59th would be eliminated, and the and merge would move from 42nd Street to 57th Street. However, with the new service pattern, an additional merge would be created with the at 36th Street. So it's the same number of merges, but I think it would be more efficient than the ones we currently have, and would de-interline one service to run alone. So I'd say it's worth it. Since the existing terminal at Bay Ridge and the future terminal at LGA likely can't handle a very high 24+ tph frequency, some trains would need to short turn at Astoria Ditmars and/or Whitehall Street. Peak direction express service could also potentially be revived on the Astoria Line since there would be the frequency to support it.
The one issue is that the train would need to hit every terminal in LGA or it wouldn't be a one seat ride. So only having one station wouldn't work. Maybe do the same thing as Howard Beach where there's a station almost entirely dedicated to the air train and has little walk up ridership. That could be located in that Con Edison lot. And what about security considerations for having the trains go directly under the airport runways. I would think the DHS, FAA, TSA would pitch a fit if the MTA even suggested doing that.
I'm normally skeptical of large scale de-interlining because it reduces the availability for one seat rides, but Broadway as it is now is just so inefficient and is an ideal candidate for it. The IND lines I think are designed to interline better, and there really aren't issues with it. I'm not sure de-interlining Brooklyn would make sense. I'm not under the impression that any of those services have capacity issues. Also, if it were de-interlined so that all Broadway trains went to 4th Avenue and all 6th Avenue trains went to Brighton, it would impose a transfer at Atlantic/Barclays that's not cross-platform since 4th Ave express trains bypass DeKalb. It's not as big of a deal if the extra transfer caused by de-interlining is cross platform. That's why I think there's no real pressure to have express one seat express service from the or line. The express trains are right across the platform at 96th or 125th if you want them.