I use the Flatbush to Knapp section as part of my bike commute from LI to Brooklyn and NEVER see topless bathers !.
When riding this path as well as driving the section east of Flatbush, I see riders all the time. Not the type of use that the Jones Beach path gets, but enough. and ton's riding down Flatbush and down to the Rockaway's via the Marine Parkway Bridge, especially in summer.
The issues with the length of time it takes to get the city to move - with Tom mentioning the section east of Pennsylvania Ave. to Howard Beach is actually about in keeping with typical city funded projects, usually measured in years. Thus I'm not at all dismayed by the length of time it took to get the most recent stuff completed, but I work for the City University and am conditioned to slow pace.
My big complaint over the years has been the lack of maintenance by the City Parks Dept., especially keeping the pathway clean, as Tom has mentioned. They do zip along the Belt,
AFAIK.
As to the Plumb Beach section, one thing that may speed things up is that the current eroded beach is all of maybe 20-25ft. from the parkway itself and THAT is something the DOT is going to have to deal with, as it will be maybe 2 more good storms before the parkway itself falls into the water.
Trouble is, the permanent fix requires a big project - rock jetties parallel to the road, a retaining wall, new surface for the path, etc... it's not going to be enough to simply plop down new asphalt as a bike path re-route.
Thus my suspicion is that it's going to be a few years before this gets restored.
SB