The Richfield bike master plan identifies this line (usually referred to as the Pleasant Ave rail line) as a preferred future trail route
I have mixed feelings on the value of this route, though the connection to Bryant bikeway is a good possibility. Personally, I'd rather see bike lanes installed on Nicollet Ave (identified by both Minneapolis and Richfield plans), or the bike lanes on Portland completed (currently a gap from 68th to 61st).
tlsbike is right that it has been discussed as part of the Dan Patch commuter rail corridor
from Northfield, through Lakeville and the immediate western suburbs of Minneapolis. However, the Pleasant Ave tracks are only an alternate choice if Edina refused to allow the train to go through their city. In any case, Dan Patch line is pretty dead, since legislators (from Edina and Bloomington) have a legal moratorium in place to prevent Mn/DOT from studying or pursuing it. Until that's lifted, there's really no fretting about it. And if/when it is, hopefully Edina can STFU and handle a little commuter rail.