Access from Roosevelt Island onto the LIRR track below the subway station is undoubtedly a pipe dream. But building a entrance to the LIRR East Side Access spur would be much easier and cheaper than ever building a new subway station connecting to either the N,R or E,V lines which each also travel underneath Roosevelt Island.
For those of you that were not aware there is another tunnel directly below the tunnel that brings the subway through Roosevelt Island. This second tunnel was built with the long term goal of bring the LIRR onto Manhattan's East Side and down into Grand Central Terminal (see the below map).
The alternatives to increasing transportation access to and from Roosevelt Island are pretty limited as we all know. So perhaps the logistics and possibility of a LIRR station stop on the Island should be investigated.
Access must exist currently to the LIRR track level for security and emergency access. What probably entered the planners minds but obviously not the pocketbooks of the MTA was the foresight to build a platform where passengers (that what LIRR straphangers are called) could board or disembark the train. It would be this cost and time required to make this pipedream even a possibility.
I am sure the technocrats would scream that security issues and that such a scope expansion would make this an impossibility. In reality we will always be seen as too small a market for anyone to care. But if Goldwater Hospital is ever razed and 10 more buildings are built on that site every alternative must be seriously looked at. This one seems the cheapest of all the subterranean options.