LRG

That's a good idea. A tunnel from Manhattan to Staten Island would be similar to the Transbay Tunnel in San Francisco's BART. Sadly, one can only be so optimistic. The much shorter 63rd St line took 20 years to complete, and wasn't linked with the QBL until 2001, 32 years after construction started.

Wouldn't there be issues with running the and on the SIR tracks, as SIR is standard railroad and operates under FRA rules while the subway doesn't?

I would also like to see a PATH extension to Grand Central or PABT-Times Square. I posted a thread on the topic, and there seemed to be some enthusiasm for the idea. However, I guess the Port Authority, unlike the MTA, is not funded by taxpayers and are less likely to act on suggestions from users of their services (not that the MTA is particularly pliable either).