Yes, this has been proposed before. My thoughts:
: Concourse-CPW Local, 6 Av Express, 4 Av Express (except rush, see ), Sea Beach Local
: Concourse Local, CPW-6 Av Express, 4 Av Express, West End Local
: Astoria Local, Broadway-Brighton Express
: 2 Av Local, Broadway Express, Brighton Local
: NEW SERVICE:
(BOLD = all times, UNDERLINED = rush hours only, ITALICS = non-rush hours only)
Broad St
Fulton Center
Chambers St
NEW STATION: Mott St
runs via a new connection from Nassau St to Manhattan Bridge
via Manhattan Bridge
Dekalb Av
Atlantic Av
Union St - rush - all times
4 Av - 9 St - rush - all times
Prospect Av - rush - all times
25 St - rush - all times
36 St
45 St - rush - all times
53 St - rush - all times
59 St
runs peak express from 8 Av to Kings Hwy, then full express from Kings Hwy to Coney Island.
8 Av
Fort Hamilton Pkwy
New Utrecht Av
18 Av
20 Av
Bay Pkwy
Kings Hwy (*see note below)
Coney Island
*Kings Hwy Station on Sea Beach would be rebuilt to have 2 island platforms.