In a speech on Monday, MTA chief Elliot Sander mentioned one possibility for increasing the capacity of New York's subway system: converting a "lightly used Bay Ridge freight line into a subway service that would run in an arc from southern Brooklyn to Queens to the Bronx."
The proposed plan, Triboro RX, would create a new line - the X train - that would run south and east of PLG, hitting other parts of Flatbush. But it would nonetheless be a boon for the area. Triboro RX would ease crowding during rush hour (by decreasing riders coming from the south on the B/Q), help reduce car traffic through large swaths of Brooklyn, and provide alternative routes for residents to get to Queens and the Bronx. Lest you think this no big deal, consider that Brooklyn's population is ever-expanding, and is only expected to rise further still in the foreseeable future.
From maps of the proposed line, it's a bit difficult to see where exactly the X train would intersect with PLG's subway lines. But it looks like it would hit the Q/B around Avenue H; and the 2/5 at Flatbush and Nostrand (Brooklyn Junction).
UPDATE: Frumination has lots more about this. Really, as much as you could possibly want to know: interactive maps, usage projections and GoogleEarth superimposed images. Spectacular stuff. (Via Brooklyn Junction).